Univorm epitaxial CoSi 2 layers have been grown in situ on a (100) Si substrate at temperatures near 600 ? C by reactive chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt, (Co(η(sup)5-C(sub)5H(sub)5) ( CO 2 ). The growth kinetics of an epitaxial CoSi 2 layer on al Si(100) substrate was investigated at temperatures ranging from 575 to 650 ? C . In initial deposition stage, plate-like discrete CoSi 2 spikes were nucleated along the directions in (100) Si substrate with a twinned structure. The discrete CoSi 2 plates with both {111} and (100) planes grew into an epitaxial layer with a flat interface on (100) Si. For epitaxial CoSi 2 growth on (100) Si, the activation energy of the parabolic growth was found to be 2.82 eV. The growth rate seems to be controlled by the diffusion of Co through the CoSi 2 layer.