Abstract: Disclosed herein is a program method of a flash memory device. In accordance with the program method, first, flash memory cells depending on the word/byte unit among flash memory cells of a memory cell array are selected. And then, the selected flash memory cells are sequentially programmed so as to have a predetermined threshold voltage which is less than a target threshold voltage. After this, the selected flash memory cells either are simultaneously programmed from the predetermined threshold voltage up to the target threshold voltage, or are divided into plural groups to be programmed sequentially. With this program algorithm, although the integration degree of the flash memory device is increased and power supply voltage level is lowered, a sufficient amount of current required to a program can be supplied without the increase of the size of an integrated circuit die.