Non-volatile memory device and erase method of the same

An erase method of a non-volatile memory device including memory cells arranged in a matrix of rows and columns. The memory cells are erased at the same time. An erase-verify operation is performed for the erased memory cells. The erase method is repeated under different bias conditions of the rows. An erase-verify operation is successively performed twice or more under different bias conditions of wordlines to decrease cell current caused by a weak cell which may be produced in a process. Thus, a reliability of an erase-verify operation is enhance to increase a yield.