METHOD OF OPERATING A FLASH MEMORY DEVICE

PURPOSE: An operation method of a flash memory is provided to prevent an error generated from back pattern dependency(BPD) by reducing the differences of currents flowing through strings in the operation of a program verification and a reading. CONSTITUTION: Word lines(WL1 to WL32) between a source selection line(SSL) and a drain selection line are divided into at least 2 word line groups. A program for a selected word line from the word lines is operated. The pass voltage of a higher level is not applied to a non-selected word lines included in the word line groups which is close to the drain selection line, but is applied to a non-selected word lines included in the word line groups which is close to the source selection line. Program verification for the selected word lines is operated.