A semiconductor device is disclosed in which resistance to the influence of external noise on internal power source network is improved. A semiconductor device operating at any predetermined frequency among a plurality thereof, and having power source networks for supplying power from a power source to internal functional units in the semiconductor device comprises switches, a storage unit, and a control unit. The switches are provided in the power source networks, and switch ON/OFF the supply of power from the power source to the functional units. In the storage unit are mapped and stored a plurality of predetermined operating frequencies and switching information designating an ON state or an OFF state for the switches. The control unit reads, from the storage, switching information corresponding to a current operating frequency, and controls the ON/OFF switching of the switches in accordance with the read switching information.