A semiconductor device including: a gain control circuit; a first circuit which is controlled a gain to be constant by the gain control circuit; and a bias circuit connected to the first circuit, wherein the first circuit including a first transistor; and a load resistance, an amplification factor or an attenuation factor of the first circuit is proportionate to a product of a transconductance of the first transistor and a resistance value of the load resistance, and a voltage applied to the load resistance is set as an output of the semiconductor device, the bias circuit generates and outputs a differential current of a current that is proportionate to a drain current flowing into the first transistor and a current that is inversely proportionate to the load resistance value, and an output of the bias circuit is connected to an output node of the first circuit.