the present invention will be described more fully hereinafter with reference to the accompanying drawings , in which typical embodiments of the invention are shown . this invention , however , may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein . rather , these embodiments are provided so that this disclosure will be thorough and complete , and will fully convey the scope of the invention to those skilled in the art . it will also be understood that when an element is referred to as being “ coupled ” or “ connected ” to another element , it can be directly coupled or connected to the other element or intervening elements may also be present . in contrast , when an element is referred to as being “ directly coupled ” or “ directly connected ” to another element , there are no intervening elements present . like numbers refer to like elements throughout . fig3 is a circuit diagram of an output buffer circuit which receives a control signal cnt , according to first embodiments of the present invention . referring to fig3 , the output buffer circuit includes a pull - up transistor 31 , a pull - down transistor 33 , a nand gate 35 , a nor gate 37 , and an inverter 39 . the pull - up transistor 31 pulls an output pin dq ( i . e ., an output terminal ) up to a supply voltage vdd in response to a pull - up control signal puc , and the pull - down transistor 33 pulls the output terminal dq down to a voltage vss ( such as a ground voltage ) in response to a pull - down control signal pdc . the nand gate 35 receives the control signal cnt and data signal data to generate the pull - up control signal puc . the nor gate 37 receives an inverse of the control signal cnt and the data signal data to generate the pull - down control signal pdc . the nand gate 35 includes a pmos transistor p 33 , a pmos transistor p 31 , a pmos transistor p 32 , an nmos transistor n 31 , and an nmos transistor n 32 . the supply voltage vdd and the reference voltage vss are connected to a source and gate of the pmos transistor p 33 , respectively . a source of the pmos transistor p 31 is connected to a drain of the pmos transistor p 33 , the data signal data is connected to a gate of the pmos transistor p 31 , and a drain of the pmos transistor p 31 is connected to an output terminal o 1 of the nand gate 35 . a source of the pmos transistor p 32 is connected to the drain of the pmos transistor p 33 , the control signal cnt is connected to a gate of the pmos transistor p 32 , and a drain of the pmos transistor p 32 is connected to the output terminal o 1 of the nand gate 35 . a drain of the nmos transistor n 31 is connected to the output terminal o 1 of the nand gate 35 , and the data signal data is connected to a gate of the nmos transistor n 31 . a drain of the nmos transistor n 32 is connected to a source of the nmos transistor n 31 , the control signal cnt is connected to a gate of the nmos transistor n 32 , and the reference voltage vss is connected to a source of the nmos transistor n 32 . the nor gate 37 includes a pmos transistor p 34 , a pmos transistor p 35 , an nmos transistor n 34 , an nmos transistor n 35 , and an nmos transistor n 36 . the supply voltage vdd is connected to a source of the pmos transistor p 34 , and the inverse cntb of the control signal cnt is connected to a gate of the pmos transistor p 34 . a source and drain of the pmos transistor p 35 are connected to a drain of the pmos transistor p 34 and an output terminal o 2 of the nor gate 37 , respectively . the data signal data is connected to a gate of the pmos transistor p 35 . a drain of the nmos transistor n 34 is connected to the output terminal o 2 of the nor gate 37 and the data signal data is connected to a gate of the nmos transistor n 34 . a drain of the nmos transistor n 35 is connected to the output terminal o 2 of the nor gate 37 , and the inverse cntb of the control signal cnt is connected to the gate of the nmos transistor n 35 . a drain of the nmos transistor n 36 is connected to a source of the nmos transistor n 34 and to a source of the nmos transistor n 35 . the supply voltage vdd and the reference voltage vss are connected to a gate and source of the nmos transistor n 36 , respectively . as mentioned above , in an output buffer circuit according to first embodiments of the present invention , two pmos transistors are present along the path between the supply voltage vdd and the output terminal o 1 of the nand gate 35 , and two pmos transistors are present along the path between the supply voltage vdd and the output terminal o 2 of the nor gate 37 . in other words , a number of pmos transistors connected in series between the supply voltage vdd and the output terminal o 1 of the nand gate 35 is equivalent to a number of pmos transistors connected in series between the supply voltage vdd and the output terminal o 2 of the nor gate 37 . similarly , two nmos transistors are present along the path between the reference voltage vss and the output terminal o 1 of the nand gate 35 , and two nmos transistors are present along the path between the reference voltage vss and the output terminal o 2 of the nor gate 37 . in other words , a number of nmos transistors connected in series between the output terminal o 1 of the nand gate 35 and the reference voltage vss is equivalent to a number of nmos transistors connected in series between the output terminal o 2 of the nor gate 37 and the reference voltage vss . accordingly , pmos transistors included in the nand gate 35 and the nor gate 37 can be fabricated to have approximately a same size ( i . e . channel width ), and further , nmos transistors can also be also fabricated to have approximately a same size ( i . e . channel width ). additionally , it is possible to fabricate the nand gate 35 and the nor gate 37 so that the input capacitance of the nand gate 35 is approximately equivalent to that of the nor gate 37 . thus , even if there are changes in process , voltage , and / or temperature ( pvt ), characteristics of the nand gate 35 can be maintained to be approximately the same as those of the nor gate 37 in an output buffer circuit according to first embodiments of the present invention , thereby reducing skew of data output via the output pin dq . fig4 is a circuit diagram of an output buffer circuit which receives a control signal cnt , according to second embodiments of the present invention . referring to fig4 , a nand gate 45 may include an nmos transistor n 33 in addition to the transistors ( p 31 , p 32 , p 33 , n 31 , and n 32 ) discussed above with respect to the nand gate 35 of fig3 . a drain of the nmos transistor n 33 is connected to an output terminal o 3 of the nand gate 45 , reference voltage vss ( such as a ground voltage ) is connected to a gate of the nmos transistor n 33 , and a source of the nmos transistor n 33 is connected to a source of an nmos transistor n 31 . in addition a nor gate 47 may include a pmos transistor p 36 in addition to the transistors ( p 34 , p 35 , n 34 , n 35 , and n 36 ) discussed above with respect to the nor gate 37 of fig3 . a source of pmos transistor p 36 is connected to a drain of a pmos transistor p 34 and a drain of pmos transistor p 36 is connected to an output terminal o 4 of the nor gate 47 . the supply voltage vdd is connected to a gate of the pmos transistor p 36 . in the output buffer circuit according to second embodiments of the present invention , a number of pmos transistors connected to the output terminal o 3 of the nand gate 45 is equal to a number of pmos transistors connected to the output terminal o 4 of the nor gate 47 . also , a number of nmos transistors connected to the output terminal o 3 of the nand gate 45 is equal to a number of nmos transistors connected to the output terminal o 4 of the nor gate 47 . more particularly , two pmos transistors and two nmos transistors are connected to the output terminals o 3 and o 4 , respectively . in addition , inner nodes of the nand gate 45 may have approximately a same capacitance as inner nodes of the nor gate 47 . for this reason , the capacitance of the output terminal o 3 of the nand gate 45 may be approximately equivalent to that of the output terminal o 4 of the nor gate 47 . accordingly , an equivalence of characteristics of the nand gate 45 and the nor gate 47 can be improved by adding nmos transistor n 33 and pmos transistor p 36 . fig5 is a circuit diagram of an output buffer circuit which receives a control signal cnt according to third embodiments of the present invention . the output buffer circuit of fig5 includes a nand gate 35 having a same structure as shown in fig3 and a nor gate 47 having a same structure as shown in fig4 . in the output buffer circuit according to third embodiments of the present invention , both an output terminal o 5 of the nand gate 35 and an output terminal o 6 of the nor gate 47 are connected to two pmos transistors p 31 and p 32 and two pmos transistors p 35 and p 36 , respectively . however , the output terminal o 5 of the nand gate 35 is connected to one nmos transistor n 32 while the output terminal o 6 of the nor gate 47 is connected to two nmos transistors n 34 and n 35 . therefore , a size ( i . e . channel width ) of the pmos transistor p 36 may be adjusted to maintain a capacitance of the output terminal o 5 of the nand gate 35 to be approximately the same as the capacitance of the output terminal o 6 of the nor gate 47 . for example , if a size ( i . e . channel width ) of each of the pmos transistors p 31 , p 32 , and p 35 is 20 μm and a size ( i . e . channel width ) of each of the nmos transistors n 31 , n 34 , and n 35 is 8 μm , a desired size ( i . e . channel width ) of the pmos transistor p 36 may be determined to be 12 μm . accordingly , an output buffer circuit according to third embodiments of the present invention may provide effects similar to those provided by second embodiments of the present invention discussed above with respect to fig4 . fig6 is a circuit diagram of an output buffer circuit which receives two control signals cnt 1 and cnt 2 according to fourth embodiments of the present invention . referring to fig6 , the output buffer circuit according to fourth embodiments of the present invention includes a pull - up transistor 31 , a pull - down transistor 33 , a nand gate 65 , a nor gate 67 , and inverters 68 and 69 . the pull - up transistor 31 pulls an output pin dq ( i . e ., an output terminal ) up to the supply voltage vdd in response to a pull - up control signal puc , and the pull - down transistor 33 pulls the output terminal dq down to the reference voltage vss in response to a pull - down control signal pdc . the nand gate 65 receives the first and second control signals cnt 1 and cnt 2 and data signal data and generates the pull - up control signal puc . the nor gate 67 receives an inverse cnt 1 b of the first control signal cnt 1 , an inverse cnt 2 b of the second control signal cnt 2 , and the data signal data and generates the pull - down control signal pdc . the nand gate 65 includes pmos transistors p 61 through p 65 and nmos transistors n 61 through n 63 . supply voltage vdd and reference voltage vss ( such as a ground voltage ) are connected to a source and gate of the pmos transistor p 64 , respectively . a source of the pmos transistor p 65 is connected to a drain of the pmos transistor p 64 , and the reference voltage , vss is connected to a gate of the pmos transistor p 65 . a source and drain of the pmos transistor p 61 are connected to a drain of the pmos transistor p 65 and the output terminal o 7 of the nand gate 65 , respectively . the data signal data is connected to a gate of the pmos transistor p 61 . a source and drain of the pmos transistor p 62 are connected to the drain of the pmos transistor p 65 and the output terminal o 7 of the nand gate 65 , respectively . the first control signal cnt 1 is connected to a gate of the pmos transistor p 62 . a source and drain of the pmos transistor p 63 are connected to the drain of the pmos transistor p 65 and the output terminal o 7 of the nand gate 65 , respectively . the second control signal cnt 2 is connected to a gate of the pmos transistor p 63 . a drain of the nmos transistor n 61 is connected to the output terminal o 7 of the nand gate 65 , and the data signal data is connected to a gate of the nmos transistor n 61 . a drain of the nmos transistor n 62 is connected to the source of the nmos transistor n 61 , and the first control signal cnt 1 is connected to a gate of the nmos transistor n 62 . a drain of the nmos transistor n 63 is connected to the source of the nmos transistor n 62 , and the second control signal cnt 2 and the reference voltage vss are connected to a gate and source of the nmos transistor n 63 , respectively . the nor gate 67 includes pmos transistors p 66 through p 68 and nmos transistors n 66 through n 70 . the supply voltage vdd and the data signal data are connected to a source and gate of the pmos transistor p 66 , respectively . a source of the pmos transistor p 67 is connected to a drain of the pmos transistor p 66 , and the inverse cnt 1 b of the first control signal cnt 1 is connected to a gate of the pmos transistor p 67 . a source and drain of the pmos transistor p 68 are connected to a drain of the pmos transistor p 67 and the output terminal o 8 of the nor gate 67 , respectively . the inverse cnt 2 b of the second control signal cnt 2 is connected to a gate of the pmos transistor p 68 . a drain of the nmos transistor n 66 is connected to the output terminal o 8 of the nor gate 67 , and the data signal data is connected to a gate of the nmos transistor n 66 . a drain of the nmos transistor n 67 is connected to the output terminal o 8 of the nor gate 67 , and the inverse cnt 1 b of the first control signal cnt 1 is connected to a gate of the nmos transistor n 67 . a drain of the nmos transistor n 68 is connected to the output terminal o 8 of the nor gate 67 , and the inverse cnt 2 b of the second control signal cnt 2 is connected to a gate of the nmos transistor n 68 . a drain of the nmos transistor n 69 is connected to sources of the nmos transistors n 66 through n 68 , and the supply voltage vdd is connected to a gate of the nmos transistor n 69 . a drain of the nmos transistor n 70 is connected to a source of the nmos transistor n 69 , and the supply voltage vdd and the reference voltage vss are connected to a gate and source of the nmos transistor n 70 , respectively . as discussed above , an output buffer circuit according to fourth embodiments of the present invention may include three pmos transistors along a path between the supply voltage vdd and the output terminal o 7 of the nand gate 65 and may include three pmos transistors along a path between the supply voltage vdd and the output terminal o 8 of the nor gate 67 . in other words , a number of pmos transistors connected in series between the supply voltage vdd and the output terminal o 7 of the nand gate 65 may be equivalent to a number of pmos transistors connected in series between the supply voltage vdd and the output terminal o 8 of the nor gate 67 . also , three nmos transistors may be present along a path between the reference voltage vss and the output terminal o 7 of the nand gate 65 , and three nmos transistors may also be present along a path between the reference voltage vss and the output terminal o 8 of the nor gate 76 . in other words , a number of nmos transistors connected in series between the output terminal o 7 of the nand gate 65 and a reference voltage vss may be equivalent to a number of nmos transistors connected in series between the output terminal o 8 of the nor gate 67 and the reference voltage vss . accordingly , sizes ( i . e . channel widths ) of pmos transistors in the nand gate 65 can be fabricated to be the same as sizes of pmos transistors in the nor gate 67 . further , sizes ( i . e . channel widths ) of nmos transistors in the nand gate 65 can be the same as those of nmos transistors in the nor gate 67 . as a result , it may be possible to maintain an input capacitance of the nand gate 65 to be approximately equivalent to that of the nor gate 67 . thus , even if there are changes in pvt in an output buffer circuit according to fourth embodiments of the present invention , characteristics of the nand gate 65 can be maintained approximately the same as those of the nor gate 67 , thereby reducing an occurrence of skew of data output via the output pin dq . fig7 is a circuit diagram of an output buffer circuit which receives two control signals cnt 1 and cnt 2 , according to fifth embodiments of the present invention . a nand gate 75 of fig7 includes an nmos transistor n 64 and an nmos transistor n 65 in addition to transistors p 61 , p 62 , p 63 , p 64 , p 65 , n 61 , n 62 and n 63 discussed above with respect to fig6 . a drain of nmos transistor n 64 is connected to an output terminal o 9 of the nand gate 75 , and a source of nmos transistor n 64 is connected to a source of an nmos transistor n 61 . a drain of the nmos transistor n 65 is connected to an output terminal o 9 of the nand gate 75 and a source of the nmos transistor n 65 is connected to the source of the nmos transistor n 61 . gates of both nmos transistors n 64 and n 65 are connected to the reference voltage vss . a nor gate 77 of fig7 includes a pmos transistor p 69 and a pmos transistor p 70 in addition to transistors p 66 , p 67 , p 68 , n 66 , n 67 , n 68 , n 69 , and n 70 discussed above with respect to fig6 . a source and drain of pmos transistor p 69 are connected to a drain of a pmos transistor p 67 and an output terminal o 10 of the nor gate 77 , respectively . supply voltage vdd is connected to a gate of the pmos transistor p 69 . a source and drain of pmos transistor p 70 are connected to the drain of the pmos transistor p 67 and the output terminal o 10 of the nor gate 77 , respectively . the supply voltage vdd is connected to a gate of the pmos transistor p 70 . accordingly , in an output buffer circuit according to fifth embodiments of the present invention , three pmos transistors are connected to the output terminal o 9 of the nand gate 75 and similarly , three pmos transistors are connected to the output terminal o 10 of the nor gate 77 . also , three nmos transistors are connected to the output terminal o 9 of the nand gate 75 and similarly , three nmos transistors are connected to the output terminal o 10 of the nor gate 77 . inner nodes of the nand gate 75 may have approximately the same capacitances as those of the nor gate 77 . as a result , a capacitance of the output terminal o 9 of the nand gate 75 is approximately equivalent to a capacitance of the output terminal o 10 of the nor gate 77 . therefore , in an output buffer circuit according to fifth embodiments of the present invention , characteristics of the nand gate 75 and the nor gate 75 can be improved with the addition of transistors n 64 , n 65 , p 69 , and p 70 . fig8 is a circuit diagram of an output buffer circuit which receives two control signals cnt 1 and cnt 2 , according to sixth embodiments of the present invention . referring to fig8 , an output buffer circuit according to the sixth embodiments of the present invention includes a nand gate 65 having a same construction as the nand gate 65 of fig6 and a nor gate 77 having a same construction as the nor gate 77 of fig7 . in an output buffer circuit according to sixth embodiments of the present invention , three pmos transistors are connected to an output terminal o 11 of the nand gate 65 and three pmos transistors are connected to an output terminal o 12 of the nor gate 77 . however , one nmos transistor is connected to the output terminal o 11 of the nand gate 65 while three nmos transistors are connected to the output terminal o 12 of the nor gate 77 . in an output buffer circuit according to sixth embodiments of the present invention , sizes ( i . e . channel widths ) of pmos transistors p 69 and p 70 may be adjusted to make the capacitance of the output terminal o 11 of the nand gate 65 approximately equivalent to that of the output terminal o 12 of the nor gate 77 . for instance , if a size ( i . e . channel width ) of each of pmos transistors p 61 , p 62 , p 63 , and p 68 is 20 μm and a size ( i . e . channel width ) of each of nmos transistors n 61 , n 66 , n 67 , and n 68 is 8 μm , a size ( i . e . channel width ) of each of the pmos transistors p 69 and p 70 may be determined to be 12 μm . further , it is possible that the functionality of pmos transistors p 69 and p 70 may be provided by a single layer pmos transistor . in this case , the size ( i . e . channel width ) of the single layer pmos transistor may be equal to the sum of the sizes ( i . e . channel width ) of the pmos transistors p 69 and p 70 . more particularly , a single layer pmos transistor having a size of 24 μm may be substituted for the transistors p 69 and p 70 of fig8 . an output buffer circuit according to sixth embodiments of the present invention may have approximately the same effects as an output buffer circuit according to fifth embodiments of the present invention . in this disclosure , embodiments of the present invention have been described with respect to an output buffer circuit that drives an output pin . embodiments of the present invention may also be applicable to buffer circuits included internally within a semiconductor device . while the present invention has been particularly shown and described with reference to embodiments thereof , it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents . as described above , even if there are changes in process , voltage , and / or temperature ( pvt ), the characteristics of a nand gate can be maintained to be approximately equivalent to those of a nor gate in an output buffer circuit according to embodiments of the present invention . accordingly an occurrence of skew of data output via an output pin may be reduced .