Method for writing multiple value into nonvolatile memory in an equal time

A method for writing a multiple value into a nonvolatile memory comprising the step of:

• writing data which take not less than three different values as threshold voltages varied according to each of the data values into a memory cell which has a gate insulating film, a floating gate, an interlayer insulating film and a control gate in order on a channel region between a source and a drain formed on a surface of a semiconductor substrate, wherein
• by applying a drain voltage varied according to each of the data values to the drain so that a write time required for setting the varied threshold voltage is equalized with a specified voltage applied to the control gate, and thereby moving electrons between the floating gate and the drain through the gate insulating film, the threshold voltage of the memory cell is set.