A manufacture process of a thin film transistor mounted on an EL display device is simplified. A thin film transistor is manufactured by stacking a first conductive film, an insulating film, a semiconductor film, an impurity semiconductor film, and a second conductive film; forming a first resist mask over the stacked films; performing first etching to form a thin-film stack body; performing second etching by side etching is conducted on the thin-film stack body to form a gate electrode layer; and forming a source and drain electrode layer and the like with use of a second resist mask. An EL display device is manufactured using the thin film transistor.