SEMICONDUCTOR DEVICE

PROBLEM TO BE SOLVED: To raise efficiency of write back processing to a nonvolatile memory transistor in an over-erasure state. SOLUTION: A semiconductor device has a plurality of pages, to each of which a plurality of nonvolatile memory transistors are assigned per wordline. In the nonvolatile memory transistor, threshold voltage is made low by erasure processing to discharge an electron from an electrical charge storage area and the threshold voltage is made high by program processing to inject the electron into the electrical charge storage area. Responding to an initialization command, a control circuit (16) performs program processing in the unit of wordline after making upper skirt of threshold voltage distribution lower than the object level by erasure processing in the unit of wordline, and before performing program processing in the unit of page for making lower skirt of the threshold voltage distribution higher than the object level. The lower skirt of the threshold voltage distribution of the nonvolatile memory transistor is raised as a whole by program processing in the unit of wordline. COPYRIGHT: (C)2007,JPO&INPIT