To obtain a DC-DC converter which controls performance degradation caused by heat generation and which has a small semiconductor module shape.

In a DC-DC converter 10, a substrate 20 formed of an insulating material is mounted on leadframes 11-16 formed of metal. In addition to the substrate 20, an inductor 31, a diode 32, a shunt resistor 33, and MOSFETs 34 and 35 are mounted in the periphery of the substrate on the leadframes 11-16. Heat generated by the inductor 31, the diode 32, and the MOSFETs 34 and 35 are efficiently dissipated by the leadframes 11, 12, 14, and 15. Control ICs 21 and 22 are mounted on the leadframe 14 via the substrate 20 formed of a material having low thermal conductivity.