A semiconductor device and a power-off method of the semiconductor device, the semiconductor device including a first power source group including first and second power sources, a second power source group including a third power source and a power sequence controller. The power sequence controller performs power-on operations and power-off operations of the first to third power sources. The power sequence controller starts a power-off operation of the first power source group at a first time, and starts a power-off operation of the second power source group when the power voltage of the first power source group becomes a first voltage or when a first reference time has passed from the first time.