Formation of epitaxial cobalt silicide film on (100)Si using Co/Ti, Co/Hf, and Co/Nb bilayers has been investigated. The degree of easiness in the epitaxial growth of CoSi2 by annealing the metal bilayers on (100)Si at 800 degreesC was found to strongly depend upon what thin metal layer was used as an epitaxy promoter. Perfect epitaxy of CoSi2 was obtained using Co/Ti/(100)Si. Local epitaxy of CoSi2 was obtained using Co/Ti/(100)Si, while epitaxy of CoSi2 was not obtained for the Co/Ti/(100)Si system. Epitaxial growth of CoSi2 in these Co/metal/Si systems seems to be related to the formation and decomposition of stable reaction barriers like Co-Ti-O and Hf-Si-O compounds at high temperatures. These stable reaction barriers formed at high temperatures make uniform diffusion of Co atoms possible, resulting in the growth of epitaxial CoSi2.