This paper will review the properties of thin silicon films deposited on sapphire (SOS) and magnesium aluminate spinel by the pyrolysis of silane in the temperature range 900-1200°C. Variations of carrier mobility, free-carrier concentration, minority carrier lifetime, crystalline perfection, and surface quality will be discussed as a function of substrate crystal and growth parameters. MOS transistors exhibiting field-effect mobility close to that obtained with bulk silicon have been fabricated and a complementary MOS transistor memory cell has been constructed with a WRITE-READ delay of 6 ns. The standby power for the cell is typically 10 µW. Other CMOS circuits display a pair-delay of 1.5-2.0 ns. AIl-epitaxial bipolar transistors with a current gain of 5 and f T of 350 MHz have been made in which all layers are sequentially deposited during one high-temperature operation. Recent improvements in bipolar fabrication techniques have lead to current gains as high as 25 at 10 mA.