Abstract: The invention concerns a semiconductor structure having a compatible mixture of bipolar and unipolar transistors. In that structure a monocrystalline p-type silicon substrate is employed which has its 1-0-0 crystallographic planes at a face on which an n epitaxial layer was grown. The epitaxial layer is divided into electrically isolated parts by V-grooves that extend down through the epitaxial layer and have their apices terminating in the substrate. A thin silicon dioxide film coats the V-grooves and those grooves are filled with polycrystallie silicon. Where it is desired to use the polycrystalline silicon as the insulated gate of a field effect transistor, the polycrystalline silicon is electrically conductive. Bases for bipolar transistors are formed by diffusion of an appropriate impurity into selected areas of the epitaxial layer. The emitters, drains, and sources are formed by diffusion of a different impurity.