A semiconductor device with a small variation in transistor characteristics is provided. The semiconductor device includes an oxide semiconductor film, a source electrode and a drain electrode over the oxide semiconductor film, an interlayer insulating film placed to cover the oxide semiconductor film, the source electrode, and the drain electrode, a first gate insulating film over the oxide semiconductor film, a second gate insulating film over the first gate insulating film, and a gate electrode over the second gate insulating film. The interlayer insulating film has an opening overlapping with a region between the source electrode and the drain electrode, the first gate insulating film, the second gate insulating film, and the gate electrode are placed in the opening of the interlayer insulating film, the first gate insulating film includes oxygen and aluminum, and the first gate insulating film includes a region thinner that is than the second gate insulating film.

Methods of depositing transition metal dichalcogenide (TMDC) films are described. The TMDC films can be used in electronic devices as, for example, a channel material in both back-end-of-line (BEOL) and front-end-of line (FEOL) applications depending on the TMDC growth temperature.