A method for producing a semiconductor power device includes forming a gate trench from a surface of the semiconductor layer toward an inside thereof. A first insulation film is formed on the inner surface of the gate trench. The method also includes removing a part on a bottom surface of the gate trench in the first insulation film. A second insulation film having a dielectric constant higher than SiO2 is formed in such a way as to cover the bottom surface of the gate trench exposed by removing the first insulation film.