A flash memory device comprises memory cells connected between a bit line and a common source line, word lines connected to the memory cells, a common source line feedback circuit connected to a common source line (CSL) to detect the voltage level of the common source line, and a CSL feedback control logic configured to control a voltage level of a selected word line or a selected bit line to be compensated to a substantially constant value during a sensing operation of the memory cells based on the detected voltage level of the CSL.