To provide a semiconductor device with a digital-controlled DC-DC converter capable of stable feedback operation while minimizing area, the semiconductor device includes a DC-DC converter whose characteristic is determined by the control parameter, a flash memory and a processor that controls the flash memory, both of which operate at a power supply based on the output of the DC-DC converter. The control parameter is stored in the flash memory, and the control parameter is read out from the flash memory and set in the DC-DC converter by the processor while the DC-DC converter is operating.