NONVOLATILE MEMORY

PROBLEM TO BE SOLVED: To increase the re-writing number of times until differential S/A24 causes erroneous discrimination or a data holding time, in a nonvolatile memory provided with a memory cell MC in which write-in and erasure of data can be performed and a reference cell RC having a threshold value becoming comparison reference when data is read out from this memory cell MC by the differential S/A24. SOLUTION: When data re-writing processing of deteriorated monitor cells EMC, PMC monitoring deterioration of the memory cell MC and the memory cell MC are performed, re-writing processing is performed for the deteriorated monitor cells EMC, PMC, stress being same as the memory cell MC is applied to the deteriorated monitor cells EMC, PMC, voltage in accordance with a threshold value of the deteriorated monitor cells EMC, PMC is applied to a control gate of the memory cell MC in order to read out data of the memory cell MC. Thereby, the threshold value of the reference cell RC is fluctuated apparently, threshold value margin is adjusted appropriately. COPYRIGHT: (C)2009,JPO&INPIT