A semiconductor device includes a pulse generation circuit which generates a pulse control signal for selectively supplying currents to the coils with the coil phases of the brushless DC motor, a selector circuit which selects arbitrary two signals, from detection signals corresponding to currents flowing respectively to the coils and a reference signal, a comparator circuit which compares the two signals selected by the selector circuit, timer counter, and a control circuit. The control circuit repeatedly controls an operation for the pulse generation circuit to output a pulse control signal for supplying electricity to one of the coil phases in a state where the rotor is stopped, an operation for the selector circuit selects the reference signal and one of the detection signals, from the detection signals.