A method for manufacturing a semiconductor device with high electric characteristics is provided. Part of a stacked semiconductor film in which an amorphous semiconductor film is provided on a crystalline semiconductor film is etched using a mixed gas including an HBr gas, a CF4 gas, and an oxygen gas, so that part of the crystalline semiconductor film provided in the stacked semiconductor film is exposed. Etching for forming a back channel portion of a thin film transistor is performed with the method for etching, whereby high electric characteristics can be provided for the thin film transistor.