In a semiconductor device according to the embodiment, a core circuit is an IC. A peripheral circuit includes a driver supplied with voltages from an internal power source and an external power source and outputting data transferred from the core circuit, and a fetch portion transferring the digital data to the driver. A first power source supplies an internal voltage to the driver via a power source line. A second power source includes current driving strings each including a current driving element and a switching element connected in series between the external power source and the power source line. The second power source supplies a current to the power source line separately from the first power source line by driving the current driving strings. A power source controller controls the second power source to drive the current driving strings when a logic transition occurs among consecutive bits of the data.