According to an embodiment, a semiconductor device includes a power supply switch and a first regulator. One end of the power supply switch is connected to an input terminal. The other end of the power supply switch is connected to an output terminal. The first regulator includes a power supply terminal connected to the one end of the power supply switch, and a voltage output terminal connected to the other end of the power supply switch. The first regulator is configured to control a voltage of the voltage output terminal to approach a target voltage based on a voltage of the power supply terminal. The target voltage is switched to a first voltage or a second voltage. The first voltage is equal to or more than the voltage of the power supply terminal. The second voltage is lower than the voltage of the power supply terminal.