Abstract: Because of process variation, there will be some voltage deviations in bandgap reference.So we need to trim the bandgap reference in ATE testing phase. An EEPROM circuit can be used to trim the Bandgap voltage. The switches parallel with the resistances can be controlled by writing trim code to EEPROM. A novel algorithm called automatic trimming is also introduced. This algorithm is able to find the best trim code only according to the initial bandgap voltage. Test time is reduced as much as 63.3 ms and accuracy can also be ensured. The bandgap test results of 300 samples are analyzed to verify the accuracy of the proposed algorithm.