The objective of the invention is to increase the yield of a manufacturing process of a semiconductor device. The objective of one embodiment of the invention is to increase the productivity of a semiconductor device. A semiconductor device is manufactured by forming a first material layer over a substrate; forming a second material layer over the first material layer; and separating the first material layer and the second material layer from each other. In addition, the first material layer and the second material layer that are stacked are heated before the separation. The first material layer includes a gas containing hydrogen, oxygen, or hydrogen and oxygen (e.g., water) in a metal oxide, for example. The second material layer includes resin. The first material layer and the second material layer are separated from each other by a break of a hydrogen bond. Water is separated out at the interface or near the interface of the first and second material layers through a heating step. Adhesion between the first and second material layers is reduced due to the existence of the water in or close to the interface so that the first and second material layers are separated from each other.