Single-crystal SrTiO 3 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 SrTiO 3 /Si interface. A regrowth of an amorphous interfacial layer as thick as 23 9 has been observed and identified as a form of SiO x . 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 9. Metal oxide semiconductor (MOS) capacitors with an equivalent oxide thickness t o x of 12 9 and a leakage current of 2x10 - 4 A/cm 2 have been obtained for a 50 9 SrTiO 3 .