A NAND flash memory device includes a memory cell array including a plurality of memory cells, a plurality of page buffers, and an isolation circuit connected between the memory cell array and the plurality of page buffers. The isolation circuit comprises a high voltage transistor adapted to disconnect a first bit line connected to the memory cell array from a second bit line connected to the one of the page buffers during an erase operation of the NAND flash memory device. During the read operation, a third bit line arranged in parallel with the second bit line and connected to one of the page buffers is discharged to prevent the page buffer from being damaged due to coupling capacitance between the second and third bit lines.