We have studied the electronic and geometric structure of thin uranium layers deposited on a clean Si(100)2 × 1 surface through X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). A formation of reacted and disordered interfaces was observed by the deposition of uranium at room temperature. Annealing of the substrate higher than 700°C results in drastic changes in the photoemission spectra and clear spots of the LEED observation. These suggest the possibility of the formation of ordered uranium silicide phases at the interface.