Abstract
A programming method of an NAND flash memory is provided, for narrowing a distribution width of a threshold voltage. The method includes a step of verification reading for verifying a threshold voltage of a selected memory cell after a programming voltage is applied to a selected word line. The verification reading further includes a step of pre-charging a voltage to a bit line, a step of discharging the pre-charged bit line to a source line, and a step of reading the voltage of the bit line after the discharging step. Regarding the discharge period from starting the discharging of the bit line to starting the read out, the discharge period of the verification reading after the initial programming voltage is applied is set longer than the discharge period of the verification reading after the subsequent programming voltage is applied.