A method of manufacturing a semiconductor device includes forming an active fin extending longitudinally in a first direction along a surface of a substrate, forming a field insulating layer on the substrate, the field insulating layer covering a part of the active fin, forming a dummy gate electrode on the field insulating layer and the active fin, the dummy gate electrode extending in a second direction different from the first direction, forming a spacer on the sides of the dummy gate electrode, and removing the dummy gate electrode by a wet etching process that includes rinsing the dummy gate electrode intermittently during an etching away of the dummy gate electrode.