A novel metal oxide is provided. One embodiment of the present invention is a crystalline metal oxide. The metal oxide includes a first layer and a second layer; the first layer has a wider bandgap than the second layer; the first layer and the second layer form a crystal lattice; and in the case where a carrier is excited in the metal oxide, the carrier is transferred through the second layer. Furthermore, the first layer contains an element M (M is one or more selected from Al, Ga, Y, and Sn) and Zn, and the second layer contains In.