Field effect transistor

A semiconductor device comprising:

• a semiconductor layer;
• a first electrode located over the semiconductor layer and connected to the semiconductor layer;
• a second electrode spaced from the first electrode and located over the semiconductor layer and connected to the semiconductor layer;
• an insulation film located over the semiconductor layer;
• and
• a third electrode interposed between the first electrode and the second electrode and located over a portion of the insulation film, wherein
• the insulation film comprises:
• a first layer comprising silicon nitride located on the semiconductor layer and between the first electrode and the second electrode, the first layer being in contact with a portion of a lower surface of the third electrode, and portions of the first electrode and the second electrode;
• and
• a second layer located on the first layer and between the first electrode and the third electrode as well as between the second electrode and the third electrode, and comprising silicon nitride and oxygen, an upper surface of the second layer substantially located in the same plane as the portion of the lower surface of the third electrode.