Exemplary embodiments of the invention provide techniques that enable avoidance of the concentration of an electric field at the edge of a semiconductor film in a semiconductor device such as a thin film transistor, thereby enhancing the reliability. Exemplary embodiments provide a method of manufacturing a semiconductor device using a structure in which a semiconductor film, a dielectric film, and an electrode are deposited. The method of manufacturing a semiconductor device includes: forming an island-shape semiconductor film on one dielectric surface of a substrate, the substrate having at least one dielectric surface; forming a first dielectric film on the one surface of the substrate so as to cover the semiconductor film and have a film thickness of the portion other than over the semiconductor film equal to or larger than that of the semiconductor film; reducing a film thickness of the first dielectric film at least in a region over the semiconductor film; and forming an electrode so as to be on the first dielectric film after reduction of the film thickness and pass over a predetermined location of the semiconductor film.