Epitaxial CoSi2 is grown on Si(100) by reaction of a Co film deposited on a Si substrate, initially separated by a thin Ti layer. Inversion of the layers and formation of a highly strained CoSi2 layer can be obtained by steady-state annealing of these Si(100)/Ti/Co structures in both reactive (N-2, N-2+ H-2, He + H-2) and nonreactive (vacuum) ambients. A reactive annealing ambient chemically binds the Ti near the surface as an oxide or nitride layer, on top of an epitaxial CoSi2 layer. This bilayer structure remains preserved during a high-temperature treatment. In a nonreactive ambient (vacuum), a similar inversion of Co and Ti is observed, as well as Si outdiffusion to the surface. At intermediate temperatures, vacuum annealing of Si(100)/Ti/Co thus results in an epitaxial CoSi2 layer on the Si substrate, capped with a layer containing Co, Ti and Si, the composition of which evolves rapidly with annealing time and/or temperature. During high-temperature treatment in vacuum, these layers react further,resulting in a uniform layer of Co0.25Ti0.75Si2 and epitaxial CoSi2.