Silicon molecular beam epitaxy (Si-MBE) has been used to produce silicon oxide (SiOx) films by evaporating Si on a heated Si(100) substrate in an ultra high vacuum system with an O-2 pressure of 10(-6) to 10(-4) mbar. Then the SiOx films were overgrown with pure Si. The influence of the substrate temperature, the O-2 pressure and the Si deposition rate on the oxygen content in the SiOx film and on the crystalline quality of the Si top-layer was investigated by Rutherford backscattering spectrometry and ion channeling. Epitaxial growth of the Si top-layer was observed up to a maximum concentration of approximate to 20 at.% oxygen content in the SiOx film. Cross-sectional transmission electron microscopy shows that the structure of the SiOx film changes during a subsequent annealing procedure. Electron energy loss spectroscopy proves that amorphous SiO2 is formed and the development of holes indicates that the density of the as-grown SiOx film is much lower than that of SiO2. The specific resistivity for the as-grown SiOx films was determined by I-V measurements.