VARIABLE CAPACITANCE ELEMENT

A variable capacitance element includes a substrate, a first semiconductor layer, a two-dimensional electron gas layer, a first electrode including a first terminal, and a second terminal. The two-dimensional electron gas layer below the first electrode functions as a second electrode. The interval between the bottom surface of the first electrode and the top surface of the first semiconductor layer monotonically increases in a first direction from the first electrode toward the second terminal or in a second direction orthogonal to the first direction. A capacitance value between the first electrode and the second electrode changes according to the voltage applied between the first electrode and the second terminal.