Single-crystal SrTiO3 has been grown on Si(100) using molecular beam epitaxy (MBE). The growth conditions. especially at the initial stage of nucleation, have a great impact on the SrTiO3/Si interface. A regrowth of an amorphous interfacial layer as thick as 23 Angstrom has been observed and identified as a form of SiOx. This is a direct result of an internal oxidation during the growth of the STO film due to the oxygen diffusion and reaction with the silicon substrate at the interface. The optimization of the deposition process in terms of growth temperature and oxygen partial pressure has led to an interfacial layer as thin as 11 Angstrom. Metal oxide semiconductor (MOS) capacitors with an equivalent oxide thickness t(ox) of 12 Angstrom and a leakage current of 2 X 10(-4) A/cm(2) have been obtained for a 50 Angstrom SrTiO3.