A novel semiconductor device is provided. The semiconductor device includes a mixer circuit and a bias circuit. The mixer circuit includes a voltage-to-current conversion portion, a current switch portion, and a current-to-voltage conversion portion. The bias circuit includes a bias supply portion and a first transistor. The voltage-to-current conversion portion includes a second transistor and a third transistor. The bias supply portion has a function of outputting a bias voltage to be supplied to a gate of the second transistor and a gate of the third transistor. One of a source and a drain of the first transistor is electrically connected to the gate of the second transistor and the gate of the third transistor. The first transistor is turned off when the bias voltage is supplied, and the first transistor is turned on when the supply of the bias voltage is stopped.