We have studied the formation of a high-quality SrTiO3 (STO) film on a Si surface which is an appropriate buffer film for fabricating high-Tc superconductor devices on Si by molecular beam epitaxy. The STO films with thicknesses of 1300–6700 Å are grown on a SrO buffer layer with a thickness of 100 Å on Si(001)-2×1 in ∼10-8 Torr. The growth temperatures for the STO films and SrO layer are 500 and 400 °C, respectively. The as-grown STO films are insufficiently oxidized regarding the Ti–O bond which is confirmed by the observation of x-ray photoemission spectroscopy, although in situ reflection high-energy electron diffraction spectroscopy and ex situ x-ray diffraction (XRD) reveal a high-quality crystalline structure. The in situ postannealing for the as-grown STO films is performed at 500–900 °C for 60 min in an oxygen atmosphere of 1×10-6 Torr. The heat treatment promotes the oxidation of STO films and results in a high resistivity of 109–1011 Ω cm and a dielectric constant of 130 at 100 kHz at room temperature. The films consist of large grains with 150–200 nm diameter on the surface in the image of atomic force microscopy. The heat treatment does not prominently affect the crystallinity of STO films in the XRD patterns. © 1999 American Institute of Physics.