A technique is described for fabricating diodes and MOS devices from vacuum deposited polycrystalline silicon films on insulating substrates. Extremely pure vacuum deposited amorphous silicon films on fused silica substrates were converted into the crystalline phase during device processing. The samples could be converted either during gaseous diffusion of boron or phosphorus at 850δ–950δC to form n‐ or p‐type layers or during the initial oxidation step at 1000δC in the device definition stage. Film purity was checked by sputter‐ion source mass spectrometry. Gaseous diffusion and oxide masking procedures were similar to those used in silicon integrated circuit technology. The quality of the initial resulting planar devices indicates that the process has the potential for producing a variety of silicon devices.