A non-insulated DC-DC converter has a power MOS•FET for a highside switch and a power MOS•FET for a lowside switch. In the non-insulated DC-DC converter, the power MOS•FET for the highside switch and the power MOS•FET for the lowside switch, driver circuits that control operations of these elements, respectively, and a Schottky barrier diode connected in parallel with the power MOS•FET for the lowside switch are respectively formed in four different semiconductor chips. These four semiconductor chips are housed in one package. The semiconductor chips are mounted over the same die pad. The semiconductor chips are disposed so as to approach each other.