By providing the metal oxide film, generation of a parasitic channel on the back channel side of the oxide semiconductor film in the transistor can be prevented.

Further, by providing the metal oxide film, generation of a parasitic channel on a back channel side of the oxide semiconductor film can be prevented in the transistor.

The spacer layer and the relaxed surface layer each have bandgap offsets relative to the buried channel layer to reduce a parasitic channel conduction.

A semiconductor device which includes an oxide semiconductor and in which formation of a parasitic channel due to a gate BT stress is suppressed is provided.