An object is to reduce power consumption of a semiconductor device including a DC-DC converter circuit. The semiconductor device includes a DC-DC converter circuit and a microprocessor. The DC-DC converter circuit includes a conversion circuit including an inductor and a transistor, and a control circuit including a comparison circuit and a logic circuit. A hysteresis comparator is used as the comparison circuit. In the control circuit, the comparison circuit compares an output signal of the conversion circuit with a first reference potential or a second reference potential, and the logic circuit performs arithmetic operation between an output signal of the comparison circuit and a clock signal of the microprocessor. In the conversion circuit, the transistor controls current flowing through the inductor in accordance with an output signal of the logic circuit, and the output signal of the conversion circuit is generated in accordance with the current flowing through the inductor.