PURPOSE: To get a small-sizedmemory unit with a good holding characteristic by piling Si3N4 or polysilicon film on SiO2 film.

CONSTITUTION: Field film oxide 11, P+ channel stopper 11A are formed on a P type Si substrate 10, a polysilicon floating gate 13 layer is made on gate film oxide 12 to be covered with film oxide 14 further laminated with a polysilicon control gate 15 layer to form gate electrodes 15, 13 by single photographic etching. Next N+ source, drain 16, 17 and a source taking out layer 16' are formed through ion injection and self-matching to make polysilicon 15, 13 conductive. Nextby selectively making an opening Al bit wiring 21 connecting with an N+ layer 17 is made. By piling Si3N4 19 with the damp-proof properties on SiO2 18 covering memory cells the gate 13 has an extremely good holding characteristic and the single photographic etching makes it possible to reduce the cell size.