in the following description , numerous specific details are set forth to provide a thorough understanding of the present invention . however , it will be obvious to those skilled in the art that the present invention may be practiced without such specific details . in other instances , well - known circuits have been shown in block diagram form in order not to obscure the present invention in unnecessary detail . for the most part , details concerning timing considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art . reference will be made to the drawing figures to describe the present invention in detail , wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by same or similar reference numeral through the several views and same or similar terminology . referring to fig1 - 3 , a first connector 1 in accordance with a preferred embodiment of the present invention is shown . in the preferred embodiment , the first connector 1 is a receptacle connector . as shown in fig1 , the first connector 1 comprises a first insulative housing 2 and a plurality of first conductive contacts 3 assembled in the first insulative housing 2 . in the preferred embodiment , there are eight first conductive contacts 3 . the first connector 1 is a power type connector for power transmission in the preferred embodiment of the present invention . however , in an alternative embodiment of the present invention , the first connector 1 is not restricted to a power type connector . in the preferred embodiment , the first insulative housing 2 comprises a rectangular first base portion 21 and a first mating portion 20 extending forwardly from middle of a front surface of the first base portion 21 . a front surface 201 of the first mating portion 20 is of elliptic shape . two rows of contact - receiving passages 22 in upper and lower relationship penetrate from the front surface 201 of the first mating portion 20 to a rear surface 210 of the first base portion 21 of the first insualtive housing 2 . a pair of arc - shape protrusions 202 extends forwardly from opposite lateral sides of the front surface 201 and each forms a contacting surface 2020 for contacting with a second connector 4 . the arc - shape protrusions 202 also can be treated as being recessed from the front surface 201 of the first mating portion 20 . now , heat - radiating structures of the first connector 1 will be introduced in detail . the heat - radiating structures comprise a third heat - radiating channel 23 , and first and second heat - radiating channels 25 , 24 which respectively communicate with the third heat - radiating channel 23 . the third heat - radiating channel 23 is defined by the front surface 201 of the first mating portion 20 and the pair of protrusions 202 . the second heat - radiating channels 24 penetrate from the front surface 201 of the first mating portion 20 to the rear surface 210 of the first base portion 21 . in the preferred embodiment , there are three second heat - radiating channels 24 . if we define an upper contact - receiving passage 22 and a lower contact - receiving passage 22 as one group , then , each second heat - radiating channel 24 is located between two groups of aligned upper and lower contact - receiving passages 22 . please refer to fig2 in particular , each second heat - radiating channel 24 communicates with the four contact - receiving passages 22 of the two groups . the first heat - radiating channels 25 are of rectangular shape and penetrate from the contacting surfaces 2020 of the protrusions 202 to the rear surface 210 of the first base portion 21 . a slot 203 for preventing from mating wrongly with the second connector 4 is defined through the left lateral wall of the first mating portion 20 . a pair of standoffs 212 is formed on the rear surface 210 of the first base portion 21 and locates adjacent to upper and lower sides of the first heat - radiating channels 25 for supporting the first insualtive housing 2 on a printed circuit board ( not shown ) and also for heat radiation . in combination with fig8 , each first conductive contact 3 comprises a first mating section 31 received in a front section of the contact - receiving passage 22 , a first retaining section 32 interferentially received in a rear section of the contact - receiving passage 22 , and a first mounting section 33 extending rearward from the first retaining section 32 and beyond the rear surface 210 of the first base portion 21 . please refer to fig2 , because the second heat - radiating channel 24 communicates with four adjacent contact - receiving passages 22 , the first retaining sections 32 of the first conductive contacts 3 are partially exposed into the second heat - radiating channel 24 . therefore , better heat radiating effect can be achieved . referring to fig4 - 6 , the second connector 4 in accordance with a preferred embodiment of the present invention is shown . in the preferred embodiment , the second connector 4 is a plug connector . as shown in fig4 , the second connector 4 comprises a second insulative housing 5 and a plurality of second conductive contacts 6 assembled to the second insulative housing 5 . in the preferred embodiment , there are eight second conductive contacts 6 . the second connector 4 is a power type connector for power transmission in the preferred embodiment of the present invention . however , in an alternative embodiment of the present invention , the second connector 4 is not restricted to a power type connector . the second insulative housing 5 comprises a rectangular second base portion 51 and a second mating portion 50 of elliptic - shape and extending from a rear surface of the second base portion 51 . the second insulative housing 5 defines two rows of contact - receiving passages 52 in upper and lower relationship which penetrate through the second base portion 51 . the second mating portion 50 comprises a mating surface 501 contacting the contacting surface 2020 of the first insualtive housing 2 . a rib 502 is formed in the inner surface of a right side wall of the second mating portion 50 and extends along front - to - back direction for mating with the slot 203 of the first insualtive housing 2 to prevent from wrong cooperation between the second and first connectors 4 , 1 . now , heat - radiating structures of the second connector 4 will be introduced in detail . the second connector 4 comprises a pair of first heat - radiating passages 55 and three second heat - radiating passages 54 . the second heat - radiating passages 54 penetrate through the second base portion 51 along front - to - back direction and each is located between two groups of aligned contact - receiving passages 52 ( the group has the same meaning as in the first connector 1 ). the first heat - radiating passages 55 are located at left and right lateral sides of the second base portion 51 and penetrate through the second base portion 51 along front - to - back direction . a pair of ribs 550 is disposed in the second base portion 51 to separate each first heat - radiating passage 55 into upper and lower halves . in combination with fig8 , the second conductive contact 6 comprises a second mating section 61 exposed into the second mating portion 50 , a second retaining section 62 interferentially received in the contact - receiving passage 52 , and an l - shape second mounting section 63 extending from the second retaining section 62 and exposed beyond a rear surface of the second base portion 51 . please refer to fig7 - 12 , an electrical connector assembly 100 in accordance with the present invention is formed by mated first and second connectors 1 , 4 . what should be pointed out is the first and second connectors 1 , 4 are the electrical connectors in accordance with the present invention . when mated , the first mating portion 20 of the first insualtive housing 2 is inserted into the second mating portion 50 of the second insualtive housing 5 until the mating surface 501 of the second mating portion 50 abuts against the front surface of the first base portion 21 with the second mating sections 61 of the second conductive contacts 6 inserted into the first mating sections 31 of the first conductive contacts 3 to form electrical connection . please refer to fig6 - 12 in particular , the electrical connector assembly 100 comprises a pair of first heat - radiating passageways 103 formed by the first heat - radiating channels 25 and the first heat - radiating passages 55 which are aligned with and communicate with one another , three second heat - radiating passageways 102 formed by the second heat - radiating channels 24 and the second heat - radiating passages 54 which are aligned with and communicate with one another , and the third heat - radiating passageway / channel 23 . therefore , after the first and second connectors 1 , 4 form electrical connection therebetween , the first and second conductive contacts 3 , 6 begin to product heat . the heat can be radiated to the outside in time ( referring to arrow directions ) through the first , second and third heat - radiating passageways 103 , 102 , 23 . the temperature of the first and second insulative housing 2 , 5 and the first and second conductive contacts 3 , 6 can be decreased effectively . please refer to fig1 , according to the directions indicated by the arrows , the heat flows from the third heat - radiating passageways 23 toward the first and second heat - radiating passageways 103 , 102 and is led out by the first and second heat - radiating passageways 103 , 102 . please refer to fig1 specially , since the contact - receiving passages 22 communicate with the second heat - radiating channels 24 partially , the heat generated by the first and second conductive contacts 3 , 6 also can be guided out from the contact - receiving passages 22 to the second heat - radiating channels 24 then to outside . at the same time , the first conductive contacts 3 partially exposed in the second heat - radiating channels 24 can be heat - radiated more effectively thus temperatures thereof can be decreased significantly . the existence of these heat - radiating passageways 102 , 103 , 23 are capable of not only radiating heat effectively to prevent the insualtive housings 2 , 5 and the conductive contacts 3 , 6 from producing different kinds of problems , but also assuring rigidity of the insulative housings 2 , 5 . it is to be understood , however , that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description , together with details of the structure and function of the invention , the disclosure is illustrative only , and changes may be made in detail , especially in matters of shape , size , and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed . for example , the tongue portion is extended in its length or is arranged on a reverse side thereof opposite to the supporting side with other contacts but still holding the contacts with an arrangement indicated by the broad general meaning of the terms in which the appended claims are expressed .