A method of manufacturing a semiconductor device includes forming a first layer on a semiconductor layer, forming a second layer on the first layer, forming a patterned mask on the second layer, etching and removing a portion of the second layer that is not covered by the patterned mask, wet etching the first layer to a width which is less than the width of the patterned mask, after the wet etching, forming an insulating layer on the semiconductor layer, removing the first layer and the second layer to form an opening in the insulating layer, and forming a gate electrode on a surface of the semiconductor layer exposed through the opening.