The Hall mobilities in 0.5 and 1.0 μm thick heteroepitaxial silicon on (11̅02) sapphire and (100) and (111) spinel substrates are compared. The substrates employed were Czochralski sapphire, alumina rich flame fusion spinel, stoichiometric Czochralski spinel, and a “modified” alumina‐rich Czochralski spinel. The semiconducting properties of the silicon on the spinels are similar if the Czochralski grown substrate surfaces are air annealed prior to deposition. The reproducibility achieved in electrical properties in silicon on spinel is related to the method of preparation of the substrate. In comparing the semiconducting properties in silicon on sapphire with silicon on spinel, one finds that the MOS transistor mobilities are more similar than the Hall mobilities.