A high-frequency device having a switching circuit includes a compound semiconductor substrate; a first high-frequency input/output terminal; a second high-frequency input/output terminal; a control signal input terminal; a power terminal; a ground terminal; an insulating portion disposed on one main surface of the compound semiconductor substrate; and a voltage-applying electrode for applying a predetermined positive voltage from the power electrode to the compound semiconductor substrate, wherein the switching circuit includes a field-effect transistor disposed on the other main surface of the active region of the compound semiconductor substrate.