It is an object to provide a method for manufacturing a thin film transistor, in which the number of masks to be used is small. A thin film transistor is manufactured as follows: a first conductive film, an insulating film, a semiconductor film, an impurity semiconductor film, and a second conductive film are stacked; a resist mask having a recessed portion is formed thereover with the use of a multi-tone mask; a thin-film stack body is formed with first etching; a gate electrode layer is formed with second etching in which an etched first conductive film is side-etched; and then a source electrode and a drain electrode and the like are formed. A crystalline semiconductor film is used for the semiconductor film.