Patent ID: 7864591

Claim:
A non-volatile semiconductor memory device comprising: a plurality of electrically data rewritable non-volatile semiconductor memory cells; a memory cell array in which a plurality of memory units are arranged in matrix, the memory unit including at least one of the memory cells; a write circuit configured to write data in a plurality of selected memory cells in the memory cells; and a write verify circuit configured to perform write verify operation for the plurality of selected memory cells by supplying a write verify voltage to gates of the plurality of selected memory cells; wherein write step operations and write verify operations are repeated when writing data into the plurality of selected memory cells, and between (n-th) write step operation and (n+1-th) write step operation (n is a natural number), a first write verify operation is performed and then a second write verify operation is performed after the first write verify operation, and wherein a first write verify voltage and a second write verify voltage are respectively supplied to the gates of the plurality of selected memory cells in the first write verify operation and the second write verify operation, the first write verify voltage is lower than the second write verify voltage; and wherein there are plurality of distributions of threshold value of the memory cells after completion of writing data in the plurality of selected memory cells, the plurality of distributions of threshold value includes a first distribution of threshold value and a second distribution of threshold value, the second distribution of threshold value has higher threshold values than the first distribution of threshold value, there is no distribution of threshold value between the first distribution of threshold value and the second distribution of threshold value, both the first write verify voltage and the second write verify voltage are higher than a center value of the first distribution of threshold value, both the first write verify voltage and the second write verify voltage are lower than a center value of the second distribution of threshold value.