An island-like semiconductor layer is formed on a main surface of an insulating substrate. A side wall of the island-like semiconductor layer is made substantially perpendicular to the insulating substrate. An insulating film is formed along the side wall of the semiconductor layer. The insulating film is formed to include a slanted face and have a sectional shape in which a width measured from the side wall of the semiconductor layer decreases as a distance to a bottom increases. A gate insulating film can be formed on the semiconductor layer with good step coverage because of inclusion of the insulating film, to preclude a possibility of causing disconnection of a gate electrode. Also, a thickness of a portion of the semiconductor layer in which a channel region is formed is uniform, to obtain stable transistor characteristics.