Semiconductor device, power supply circuit, and computer

A semiconductor device comprising:

• a first nitride semiconductor layer;
• a second nitride semiconductor layer disposed on the first nitride semiconductor layer and having a larger bandgap than that of the first nitride semiconductor layer;
• a first electrode disposed on or above the first nitride semiconductor layer and electrically connected to the first nitride semiconductor layer;
• a second electrode disposed on or above the first nitride semiconductor layer and electrically connected to the first nitride semiconductor layer;
• a gate electrode disposed above the first nitride semiconductor layer, the gate electrode disposed between the first electrode and the second electrode;
• and
• a gate insulating layer disposed between the first nitride semiconductor layer and the gate electrode, the gate insulating layer including a silicon oxide film and an aluminum oxynitride film, the aluminum oxynitride film disposed between the first nitride semiconductor layer and the silicon oxide film, a first atomic ratio of nitrogen relative to a sum of oxygen and nitrogen at a first position in the aluminum oxynitride film being higher than a second atomic ratio of nitrogen relative to a sum of oxygen and nitrogen at a second position in the aluminum oxynitride film, and the second position being closer to the silicon oxide film than the first position.