A method for processing an oxide semiconductor containing indium, gallium, and zinc is provided. In the method, the oxide semiconductor layer comprises a plurality of excess oxygen, a first oxygen vacancy that is close to first indium and captures first hydrogen, and a second oxygen vacancy that is close to second indium and captures second hydrogen, the first hydrogen captured by the first oxygen vacancy is bonded to one of a plurality of excess oxygen to so that a hydroxyl is formed; the hydroxyl is bonded to the second hydrogen captured by the second oxygen vacancy to release as water; and then, the first oxygen vacancy captures one of excess oxygen and the second oxygen vacancy captures one of excess oxygen.