A high voltage/power semiconductor device has a substrate, an insulating layer on the substrate, and a semiconductor layer on the insulating layer. Low and high voltage terminals are connected to the semiconductor layer. The device has a control terminal. The semiconductor layer includes a drift region and a relatively highly doped injector region between the drift region and the high voltage terminal. The device has a relatively highly doped region in electrical contact with the highly doped injector region and the high voltage terminal and forming a semiconductor junction with the substrate. The combination of the insulating layer and the relatively highly doped region of the first conductivity type effectively isolate the highly doped injector region from the substrate.