A semiconductor device for vector control of an AC motor via an inverter, includes a dq-axis reference current value generator which generates dq-axis reference current values, a three-phase/two-phase converter which generates dq-axis detected current values from three-phase current values of the inverter and a rotor position of the AC motor, a current controller generates dq-axis reference voltage values by proportional control and proportional integral control based on the dq-axis reference current values, the dq-axis detected current values, a rotation angular speed of the AC motor, and a motor parameter setting value, wherein the integration controller provides an initial voltage value to an integrator before switching to the proportional integral control, and wherein the initial voltage value is based on the dq-axis reference current values, the dq-axis detected current values, the rotation angular speed, the motor parameter setting value, and one of a proportional gain and the dq-axis reference voltage values.