A non-volatile semiconductor memory device includes a memory cell array with electrically rewritable non-volatile memory cells laid out therein, an address selector circuit for performing memory cell selection of the memory cell array, a data read/write circuit arranged to perform data read of the memory cell array and data write to the memory cell array, and a control circuit for executing a series of copy write operations in such a manner that a data output operation of from the data read/write circuit to outside of a chip and a data write operation of from the data read/write circuit to the memory cell array are overlapped each other, the copy write operation including reading data at a certain address of the memory cell array into the data read/write circuit, outputting read data held in the read/write circuit to outside of the chip and writing write data into another address of the memory cell array, the write data being a modified version of the read data held in the data read/write circuit as externally created outside the chip.