To provide a semiconductor device that more surely prevents heat transfer from a first semiconductor device with a high operating temperature to a second semiconductor device with a low operating temperature via a lead frame more.

A semiconductor device is provided with a first lead frame 20 with a power element 25 with a relatively high operating temperature mounted; a second lead frame 30 that is juxtaposed with the first lead frame clear of it and has a control element 35 with a relatively low operating temperature mounted; thermal resistances 15 and 16 interposed in a clearance 40 between the outer edge 21a of the first lead frame and the outer edge 31a of the second lead frame; and a temperature-sensitive element 26 detecting the temperature of the first semiconductor device and informing the second semiconductor device of detection results. The heat transfer, from the first lead frame to the second lead frame, is suppressed by the thermal resistances. When the temperature of the first semiconductor device detected by the temperature-sensitive element exceeds a predetermined value, the second semiconductor device restricts the operation of the first semiconductor device.