A method for fabricating a single crystal silicon on insulator material by forming oxidized layers underneath epi islands without damaging the surface quality of the silicon. In an illustrative embodiment, an epitaxial layer of p-type silicon is grown on a substrate of n-type silicon. A plurality of islands are defined from the epitaxial layer. A semiconductor device is fabricated from one of the p-islands by electrochemically anodizing a region of the substrate beneath that p-island, which p-island can be used to fabricate a selected semiconductor device. If n-type material is required for device fabrication, a device layer of n-type silicon can be grown on the surface of a p-islands and that p-island can be anodized and oxidized to form the insulating layer between the device layer and substrate. In this manner, MOS transistors and other devices may be fabricated for operation at temperatures of up to 500.degree. C.