Epitaxial CoSi2(100) layers in the thickness range of 20 to 50 nm have been formed by reactive deposition epitaxy (i.e. Co deposition onto a hot Si substrate) without the use of either a template or an intermediate Ti layer. It is explained how growth parameters such as the deposition rate and substrate temperature are crucial in determining the epitaxial nature of the silicide. According to this model, good CoSi2/Si(100) alignment is only achieved when very low deposition rates are used (0.1 Å/s or less), combined with relatively high substrate temperatures during deposition (∼ 600°C or higher). Using these conditions, highly strained, continuous CoSi2 layers with a channeling minimum yield of χmin = 9% could be formed. Using higher rates and/or lower deposition temperatures, an increasing fraction of misoriented CoSi2 grains is presumed from backscattering/channeling and x-ray experiments, the nature of which is under investigation with plan view and cross sectional transmission electron microscopy.