An epitaxial CoSi2 layer was grown on Si(100) substrate by the diffusion of Co from a cobalt-carbon film without the use of an interlayer, which is usually required between the Si and cobalt layers for the formation of epitaxial CoSi2 layers. Co-C and pure Co layers were deposited by metallorganic chemical vapor deposition using the Co precursor cyclopentadienyl dicarbonyl cobalt, Co(eta(5)-C5H5)(CO)(2), and cobalt carbonyl, Co-2(CO)(8), at 350 and 200 degrees C, respectively. The CoSi2 layer was epitaxially grown on Si(100) substrate from Co-C by ex situ rapid thermal annealing at 800 degrees C in N-2 ambient. However, the polycrystalline CoSi2 layer was formed from pure Co film under the same annealing conditions. The supply of Co to the interface by diffusion in the Co-C film seems to be lower enough than in the pure Co film, resulting in an epitaxial CoSi2 layer on Si(100) substrate.