To provide a highly reliable and low-power-consumption semiconductor device functioning as a programmable logic device. A monitor circuit is provided to monitor a change in the potential of a configuration memory in which a transistor is turned off to hold charge and a potential corresponding to the charge is stored as configuration data. The reset of the configuration data is controlled in accordance with the potential change. With such a structure, the configuration memory can be reconfigured before the configuration data is lost, resulting in improved reliability of the semiconductor device. In addition, reconfiguration can be performed every time data is lost. Accordingly, power consumption can be reduced as compared with the structure where reconfiguration is performed periodically.