the present invention relates to a method and apparatus for trimming a reference voltage . the method may include at least one steep of performing an erase operation of a flash memory resistor ; performing a program operation of the flash memory resistor ; performing a current read operation of the flash memory resistor ; confirming the threshold voltage of the flash memory resistor by measuring the current flowing into a drain of the flash memory resistor ; determining whether the threshold voltage of the flash memory resistor satisfies a reference voltage ; and then completing the trimming operation if the threshold voltage of the flash memory resistor satisfies the reference voltage .