Nonvolatile semiconductor memory device

摘要

A threshold voltage distribution D2 apparently decreases to'a distribution D3 when there is a distribution D1 of memory cells having deep depletion. After an erase is performed utilizing an erase determination level 1 higher than a desired erase determination level 2, only data in memory cells of distribution D1 is rewritten utilizing a rewrite determination level 1 lower than a desired rewrite determination level 2. The erase is performed utilizing erase determination level 2 since the threshold voltage distribution shifts a distribution D7 by canceling the effect caused by the memory cells having deep depletion, and only data in the memory cells having shallow depletion is rewritten.