Nonvolatile semiconductor memory device including sense amplifier having

Abstract

The object of the present invention is to reduce the dispersion of the threshold after writing while maintaining the high speed nature of a write system in a nonvolatile semiconductor memory such as a flash memory of channel hot electron write type. The feature of this invention is to provide a memory with a write current detection type write circuit and a sense amplifier for read, and to switch, for verification at the time of write, between verification by the write current type write circuit and verification of normal read mode which uses the sense amplifier for read. In other words, when a cell threshold of write level is designated as a first threshold and a specified threshold level lower than the first threshold is designated as a second threshold, write operation by the write current detection type write circuit is performed at the beginning of write mode, and stops the write operation when the current flowing between the drain and the source of the memory cell falls to below or equal to the reference current corresponding to the second threshold. Thereafter, the write operation is performed by repeating the write operation and verification operation using the sense amplifier until the cell threshold reaches the first threshold.