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.

A nanowire device includes one or more nanowire having a first end portion, a second end portion, and a body portion between the first end portion and the second end portion. A first conductive structure is in contact with the first end portion and a second conductive structure is in contact with the second end portion. The body portion of the nanowire has a first cross-sectional shape and the first end portion has a second cross-sectional shape different from the first cross-sectional shape. Integrated circuits including the nanowire device and a method of cleaning a semiconductor structure are also disclosed.