Various devices have been fabricated using silicon films grown epitaxially on low aluminum-rich spinel substrates. The insulating substrate provides complete isolation of the semiconductor devices and eliminates the parasitic capacitances of the back-biased p− n junctions. The low aluminum-rich spinel offers the advantages of better thermal stability and easier surface preparation for silicon epitaxy over both the conventional high aluminum-rich (MgO:3Al 2O 3) and the stoichiometric (MgO:Al 2O 3) materials. MOS capacitors, MOS transistors, and vertical junction diodes were constructed and studied using films with mobilities equal to or near the bulk values. Information on MOS capacitance vs. bias behavior, transistor characteristics, diode junction properties, and minority carrier lifetime was obtained. The silicon-spinel composites were also characterized by physical methods, and the nature of the defect structures was examined.