Details of the molecular beam epitaxial growth of osmium silicide (OsSi2 and Os2Si3) thin films are presented. The study has been motivated by reports that OsSi2 has a band gap between 1.4-1.8 eV [L. Schellenberg et al., J. Less-Common Met. 144, 341 (1988); K. Mason and G. Muller-Vogt, J. Cryst. Growth 63, 34 (1983)], and Os2Si3 has a band gap of 0.95 eV [A. B. Filonov et al., Phys. Rev. B 60, 16494 (1999)] or 2.3 eV [L. Schellenberg et al., J. Less-Common Met. 144, 341 (1988)]. Of particular note is that the OS2S'3 band gap is predicted to be direct, and thus has significant potential optoelectronic applications. The resulting films have been analyzed using reflection high-energy electron diffraction, scanning electron microscopy, x-ray reflectivity measurements, and out-of-plane x-ray diffraction. For low Si/Os flux ratios (similar to 1.5), both OsSi2 and Os2Si3 phases are observed. However, with a larger Si/Os flux ratio (similar to 4) the crystalline quality is greatly increased and only a single phase Os2Si3 is observed. We present our results and discuss our observations in relation to thermodynamic considerations and growth parameters. (c) 2006 American Vacuum Society.