Abstract: A highly reliable semiconductor device is provided. Over an oxide semiconductor layer in which a channel is formed, an insulating layer including the oxide semiconductor material having a higher insulating property than an oxide semiconductor layer is formed. A material which contains an element M and is represented by a chemical formula InMZnOX (X>0) or an oxide material which contains an element M1 and an element M2 and is represented by a chemical formula InM1XM2(1?X)ZnO (0<X<1+? where ? is less than 0.3 and (1?X)>0) is used as the oxide semiconductor material having a high insulating property. Ti, Zr, Hf, Ge, Ce, or Y is used as the element M and the element M2, for example. Ga is used as the element M1, for example.