A semiconductor device includes a connector connectable to a host, a power supply circuit which includes an input portion that receives first power from the host via the connector, an output portion, and a switch that is connected to the input portion and the output portion and controls whether to supply the first power to the output portion, the power supply circuit generating second power and third power from the first power, a semiconductor memory which receives the second power from the output portion, and a controller which receives the third power from the output portion and controls the semiconductor memory. The power supply circuit turns off the switch and stops supply of power to the semiconductor memory and the controller when the second power exceeds a first value or when the third power exceeds a second value.