It is an object of the present invention to enhance a selection ratio in an etching process, and provide a method for manufacturing a semiconductor device that has favorable uniform characteristics with high yield. In a method for manufacturing a semiconductor device according to the present invention, a semiconductor layer is formed, a gate insulating film is formed on the semiconductor film, a first conductive layer is formed on the gate insulating film, a second conductive layer is formed on the first conductive layer, the first conductive layer and the second conductive layer are etched to form a first conductive-layer pattern, the second conductive layer in the first conductive-layer pattern is selectively etched with plasma of boron trichloride, chlorine, and oxygen to form a second conductive-layer pattern, and a first impurity region and a second impurity region are formed in the semiconductor layer.