Disclosed herein is an erase method of a flash memory device that comprises discrete first and second erase discrimination periods. An erase operation is carried out using a bulk stepping scheme during the first erase discrimination period while the erase operation is carried out using a fixed bulk voltage during the second erase discrimination period. According to this method, the number of over-erased memory cells caused by the bad erase property is reduced, so that a total erase time of the flash memory device can be reduced and over-erase can be prevented.