Polycrystalline Al2O3 thin films have been grown on Si substrates by ionized beam deposition using an aluminum solid source in O-2 environments. To prevent the aluminum interdiffusion to Si at high substrate temperature (T-s > 500 degreesC), the oxidized Al prelayer with a thickness of 3 nm was deposited on the Si substrate at room temperature before Al2O3 deposition, and subsequently polycrystalline Al2O3 films were grown at 700 degreesC. Although Al interdiffusion increased at the interface with increasing T,, the oxidized Al prelayer was effective as a buffer layer on which to grow stoichiometric and crystalline Al2O3 films up to T-s= 800 degreesC.