The invention relates to a semiconductor device. Usage of a closed APC can refer to the cost and power consumption problems caused by the increased circuit scale. The semiconductor device includes a power amplifier that amplifies an output from a transmission circuit and a regulator that supplies power to the power amplifier. The regulator includes an operational amplifier comprising a loop gain control circuit and a loop gain control voltage generation circuit that supplies control voltage to the loop gain control circuit. The loop gain control voltage generation circuit minimizes a loop gainof the operational amplifier when starting up the regulator.