a phosphorus doped amorphous silicon film 14 is deposited here 1 is a silicon substrate 2 is a tunnel oxide film and 3 is an element isolating silicon oxide film the phosphorus doped amorphous silicon film 14 can be formed for example by the thermal cvd method using monosilane sih 4 and phosphine ph 3 at 500 550 u00b0 c the phosphorus content in the phosphorus doped amorphous silicon film 14 can be controlled by changing the ratio of flow rates of monosilane sih 4 and phosphine ph 3 next referring to fig2 b the phosphorus doped amorphous silicon film 14 deposited in fig2 a is processed into a desired shape by lithography and dry etching method referring to fig2 c the phosphorus doped amorphous silicon film 14 is annealed in an no gas or no gas containing atmosphere at 850 1150 u00b0 c at this time the phosphorus doped amorphous silicon film 14 is converted to a floating gate electrode 5 consisting of a phosphorus doped polycrystalline silicon by thermal energy and a silicon nitride film layer 6 is further formed on this floating gate electrode 5 next referring to fig2 d a cvd silicon oxide film 15 is formed by the thermal cvd method using monosilane sih 4 and dinitrogen monoxide n 2 o dichlorosilane sih 2 cl 2 and dinitrogen monoxide n 2 o or the like at 700 900 u00b0 c referring now to the following fig2 e a dense silicon oxide film 7 is formed by annealing the cvd silicon oxide film 15 in a steam atmosphere at this time since.