Abstract: A method of forming a semiconductor device having a single crystal silicon substrate, the surface of which includes exposed silicon areas bounded by and coplanar with insulating oxide regions. A polysilicon layer is deposited thereon and annealed to form a single crystal epitaxial region overlying the exposed substrate areas while the regions overlying the oxide areas in the substrate surface may be of polycrystalline form. This structure is applied to NMOS, CMOS, MESFET, and I.sup.2 L devices to achieve high packing density, high speed, improved isolation between devices and reduced susceptibility to latch-up.