To provide a metal base circuit substrate imparted with folding and drawing processes, which is able to reconcile cracks in an insulating layer of withstand voltage, with a low thermal resistance, and provide a method of manufacturing the substrate.

The metal base circuit substrate is provided with a circuit 3 on a metal plate 1 with an insulating layer 2 made of resin comprising a ceramics filler interposed therebetween. The metal plate at least has a non-flat portion, with a thermal resistance being not more than 2.0°C/W and not less than 0.8 kV. Folding and/or drawing process(es) are/is carried out at a temperature which is higher by 10°C than a transition temperature of the glass in the insulating layer 2.