Nonvolatile semiconductor memory device which stores two bits per memory cell

摘要

A nonvolatile semiconductor memory device includes nonvolatile memory cells each configured to store 2-bit information per memory cell, and a control circuit configured to verify with a first threshold one or more bits subjected to writing of new data and to verify with a second threshold one or more bits subjected to refreshing of existing data in a program operation that performs the writing of new data and the refreshing of existing data simultaneously with respect to the nonvolatile memory cells, the second threshold being lower than the first threshold.