The SrTiO3/Si interface was investigated by transmission electron microscopy for SrTiO3 films grown on (001) Si by molecular-beam epitaxy with different native oxide (SiO2) removal treatments, and Sr/Ti flux ratios. The interface and film microstructure were independent of the process used to remove the native oxide, but the interface reactivity was dependent on the Sr/Ti flux ratio. A low Sr/Ti flux ratio (similar to 0.8) resulted not only in a layer of amorphous material at the film/substrate interface but also in the formation of crystalline C49 TiSi2 precipitates at that interface. These results are consistent with thermodynamic expectations in which it is paramount to maintain separation between TiO2 and the underlying silicon. (c) 2005 American Institute of Physics.