An object is to provide a method for manufacturing a highly reliable semiconductor device including thin film transistors which have stable electric characteristics and are formed using an oxide semiconductor. A method for manufacturing a semiconductor device includes the steps of: forming an oxide semiconductor film over a gate electrode with a gate insulating film interposed between the oxide semiconductor film and the gate electrode, over an insulating surface; forming a first conductive film including at least one of titanium, molybdenum, and tungsten, over the oxide semiconductor film; forming a second conductive film including a metal having lower electronegativity than hydrogen, over the first conductive film; forming a source electrode and a drain electrode by etching of the first conductive film and the second conductive film; and forming an insulating film in contact with the oxide semiconductor film, over the oxide semiconductor film, the source electrode, and the drain electrode.