NONVOLATILE SEMICONDUCTOR MEMORY DEVICE

The disclosed invention provides a technique for efficiently avoiding read disturbance. A nonvolatile semiconductor memory device includes a nonvolatile memory unit and a controller that can control refresh processing for rewriting data in a block of blocks assumed to be erasable units in the nonvolatile memory unit into anther block different from the block. The controller sets up a first area and a second area different from the first area in the nonvolatile memory unit and, each time a refresh trigger occurs, executes refresh processing for the first area and the second area, such that a refresh frequency of data in the first area will become higher than a refresh frequency of data in the second area. Thereby, it is possible to efficiently avoid read disturbance when read access is repeated.