The structure is very similar to that of a vertically diffused MOSFET featuring a double diffusion of a p-type region and an n-type region. An inversion layer can be formed under the gate by applying the correct voltage to the gate contact as with a MOSFET. The main difference is the use of a p
+ substrate layer for the drain. The effect is to change this into a bipolar device as this p-type region injects holes into the n-type drift region.
