A method for operating a flash memory device includes applying a pass voltage to a drain pass word line, a source pass word line, and unselected word lines. The drain pass word line is provided between a drain select line and a word line. The drain pass word line has a structure in the same manner as the word lines. The source pass word line is provided between a source select line and a word line. The source pass word line has a structure in the same manner as the word lines. A program voltage is applied to a selected word line associated with a selected memory cell block. A ground voltage is applied to drain pass word lines and source pass word lines. Word lines associated with unselected memory cell blocks are set to a floating state.