Provided is a semiconductor device having a structure with which a decrease in electrical characteristics that becomes more significant with miniaturization can be suppressed. The semiconductor device includes a first oxide semiconductor film, a gate electrode overlapping with the first oxide semiconductor film, a first gate insulating film between the first oxide semiconductor film and the gate electrode, and a second gate insulating film between the first gate insulating film and the gate electrode. In the first gate insulating film, a peak appears at a diffraction angle 2θ of around 28° by X-ray diffraction. A band gap of the first oxide semiconductor film is smaller than a band gap of the first gate insulating film, and the band gap of the first gate insulating film is smaller than a band gap of the second gate insulating film.