Epitaxial films of cobalt silicide grown on (001) Si by molecular beam epitaxy have been characterized by transmission electron microscopy. Apart from (001) oriented CoSi2 grains, regions of 〈221〉 type orientations were also found. The 〈221〉 oriented domains were found to be associated with pronounced facetted depressions on the (001) Si surface. Empirical observations suggest that the formation of 〈221〉 CoSi 2 domains and the formation of other types of silicide stoichiometries may be related. It is demonstrated that these microstructural instabilities may be suppressed by the codeposition of cobalt and silicon rather than simply by depositing cobalt and reacting with the Si substrate to produce (001) CoSi2.