An object of the present invention to provide a highly reliable semiconductor device. Another object is to provide a manufacturing method of a highly reliable semiconductor device. Still another object is to provide a semiconductor device having low power consumption. Yet another object is to provide a manufacturing method of a semiconductor device having low power consumption. Furthermore, another object is to provide a semiconductor device which can be manufactured with high mass productivity. Another object is to provide a manufacturing method of a semiconductor device which can be manufactured with high mass productivity. An impurity remaining in an oxide semiconductor layer is removed so that the oxide semiconductor layer is purified to have an extremely high purity. Specifically, after adding a halogen element into the oxide semiconductor layer, heat treatment is performed to remove an impurity from the oxide semiconductor layer. The halogen element is preferably fluorine.