A semiconductor device connectable between a first power-supply line connected to a power source and through which power is continuously supplied to a first circuit, and a second power-supply line that is not directly connected to the power source and is connected to a second circuit, includes a first switch connectable between the first and second power-supply lines and turned on in response to a signal for supplying power to the second circuit, a second switch connectable between the first and second power-supply lines and having a current supply capability higher than the first switch, and a control circuit configured to turn on the second switch when the first switch is turned on and a voltage applied to the second power-supply line has reached a threshold.