A semiconductor device includes a p-channel MIS transistor. A p-channel MIS transistor includes; an n-type semiconductor layer formed on the substrate; first source/drain regions being formed in the n-type semiconductor layer and being separated from each other; a first gate insulating film being formed on the n-type semiconductor layer between the first source/drain regions, and containing silicon, oxygen, and nitrogen, or containing silicon and nitrogen; a first gate electrode formed above the first gate insulating film; and a first interfacial layer being formed at an interface between the first gate insulating film and the first gate electrode, and containing a 13-group element. The total number of metallic bonds in the 13-group element in the interfacial layer being larger than the total number of each of oxidized, nitrided, or oxynitrided bonds in the 13-group element in the interfacial layer.