A semiconductor device according to the present invention includes a semiconductor layer. A first conductivity type region is formed on a base layer portion of the semiconductor layer. A body region of a second conductivity type is formed on the semiconductor layer to be in contact with the first conductivity type region. A trench in which a gate electrode is embedded through a gate insulating film is formed on the semiconductor layer. The trench penetrates through the body region, so that a deepest portion thereof reaches the first conductivity type region. A source region of the first conductivity type is formed on a surface layer portion of the semiconductor layer around the trench. The gate insulating film includes a thick-film portion having a relatively large thickness on a bottom surface of the trench.