Abstract: A non-volatile semiconductor memory includes a plurality of memory cells. Each memory cell includes N-type source and drain regions formed in a P-well on a semiconductor substrate, a floating gate formed on the P-well with a tunnel oxide film therebetween, and a control gate formed on the floating gate with an interpoly dielectric film therebetween. The memory has a plurality of bit lines, a plurality of word lines and a source line. The source region of each memory cell is connected to the source line. The drain region of each memory cell is connected to one of the word lines. The memory cell is written to, erased, or read by selectively supplying suitable voltages to the source, bit, and word lines connected thereto.

Abstract: There is provided a method for writing a multiple value into a nonvolatile memory capable of writing multiple value data into a floating gate type memory cell in an equal time even when the data are varied. With a specified voltage applied to a control gate of a memory cell, a drain voltage which is varied according to each of data values "11", "10" and "01" to a drain so that a write time required for setting a varied threshold voltage is equalized. By moving electrons between a floating gate and a drain through a gate insulating film, the threshold voltage of the memory cell is set.