To provide a method for forming a dielectric film between gates of a flash memory element capable of preventing a change in thickness of the dielectric film by suppressing a reaction between a floating gate and an oxide film.

The method for forming the dielectric film comprises the steps of forming a silicon film pattern making a floating gate, forming a silicon-fluorine coupling layer on the surface of the silicon film pattern in a fluorine-supplying atmosphere, forming a silicon-nitride coupling layer on the surface of the silicon film pattern by heat treating in a nitride atmosphere, forming a dielectric film including at least one-layer oxide film on the silicon film pattern having a silicon-nitride coupling layer, and forming a condutive film for forming a control gate on the dielectric film.