The temperature dependence of electron and Hall mobilities in accumulation and inversion layers is presented for silicon‐on‐sapphire films. The inversion‐layer mobilities, as a function of surface carrier density, are also given. It is suggested that the reduced mobility resulting in these layers is due to silicon‐oxygen complexes located near the film surface. From the data presented, it is expected that deep‐depletionn‐channel transistors will have approximately 40&percent; higher effective mobilities than conventional inversion‐moden‐channel devices on sapphire.