In a miniaturized field effect transistor, the roughness of the interface between a gate dielectric film and a gate electrode is controlled on an atomic scale. The thickness variation of the gate dielectric film is lowered, whereby a field effect transistor with high mobility is manufactured. An increase in the mobility in the field effect transistor can be achieved not only in the case of using a conventional SiO2 thermal oxide film as the gate dielectric film but also in the case of using a high dielectric material for the gate dielectric film.