The amount of data to be backed up and recovered is reduced when supply of power to a semiconductor device is stopped and restarted. A backup need determination circuit provided in the semiconductor device reads the kind of instruction decoded by a decoder and determines whether data needs to be backed up from a volatile register to a nonvolatile register. With a structure according to one embodiment of the present invention, it is possible to select necessary data from data used for operation in a logic circuit before the power supply is stopped and after the power supply is restarted. Data that is necessary after the power supply is restarted can be backed up from the volatile register to the nonvolatile register before the power supply is stopped. Data that is unnecessary is not backed up from the volatile register to the nonvolatile register before the power supply is stopped.