Semiconductor device in which an injector region is isolated from a substrate

A high voltage/power semiconductor device, the device comprising:

• a relatively lowly doped substrate;
• an insulating layer on the substrate;
• a semiconductor layer on the insulating layer;
• a low voltage terminal and a high voltage terminal each electrically connected to the semiconductor layer;
• a control terminal;
• the semiconductor layer including a drift region of a first conductivity type, the substrate being of the second conductivity type;
• the semiconductor layer including a relatively highly doped injector region of the second conductivity type between the drift region and the high voltage terminal, said relatively highly doped injector region being in electrical contact with the high voltage terminal and not being physically connected via any semiconductor layer to the substrate;
• and,
• a relatively highly doped region of the first conductivity type in electrical contact with the said relatively 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 isolating the relatively highly doped injector region from the substrate.