The invention relates to a method of fabricating a flash memory device. According to the method, select transistors and memory cells are formed on, and junctions are formed in a semiconductor substrate. The semiconductor substrate between a select transistor and an adjacent memory cell are over etched using a hard mask pattern. Accordingly, migration of electrons can be prohibited and program disturbance characteristics can be improved. Further, a void is formed between the memory cells. Accordingly, an interference phenomenon between the memory cells can be reduced and, therefore, the reliability of a flash memory device can be improved.