A field effect transistor includes a first semiconductor layer made of a multilayer of a plurality of semiconductor films and a second semiconductor layer formed on the first semiconductor layer. A source electrode and a drain electrode are formed on the second semiconductor layer to be spaced from each other. An opening having an insulating film on its inner wall is formed in a portion of the second semiconductor layer sandwiched between the source electrode and the drain electrode so as to expose the first semiconductor layer therein. A gate electrode is formed in the opening to be in contact with the insulating film and the first semiconductor layer on the bottom of the opening.