US Patent 7492643 Nonvolatile semiconductor memory

A nonvolatile semiconductor memory according to an example of the present invention comprises a memory cell array composed of a plurality of memory cells, an internal circuit which writes into the plurality of memory cells by use of one of a first mode in which a first threshold distribution can be obtained and a second mode in which a second threshold distribution different from the first threshold distribution can be obtained, and a threshold distribution control circuit which controls switchover between the first mode and the second mode.