To provide a semiconductor device having improved reliability. The semiconductor device has, on a SOI substrate thereof having a semiconductor substrate, an insulating layer, and a semiconductor layer, a gate insulating film having an insulating film and a high dielectric constant film. The high dielectric constant film has a higher dielectric constant than a silicon oxide film and includes a first metal and a second metal. In the high dielectric constant film, the ratio of the number of atoms of the first metal to the total number of atoms of the first metal and the second metal is equal to or more than 75%, and less than 100%.