A coupling oxide film is formed on a silicon substrate, a polysilicon film is further formed thereupon, and a low-temperature oxide film is deposited to a thickness of 10 nm, for example. Next, a silicon nitride film is formed on this low-temperature oxide film, and selectively removed by dry etching. At this time, the low-temperature oxide film serves as an etching stopper film, so the low-temperature oxide film and polysilicon film are not over-etched. Subsequently, the polysilicon film is dry-etched, forming a recess. A floating gate is then formed of the polysilicon film.