Evaporated Si grew epitaxially on Si(100) at approximately 500 o C when very thin Ni layers were deposited on the substrate even under a medium vacuum condition of 10 - 7 torr. Cross-sectional TEM and electron diffraction showed the formation of a thin and uniform epitaxial NiSi 2 layer on the Si substrate. Thus the Ni enhanced low-temperature Si epitaxial growth can be explained by a Si/NiSi 2 /Si hetero-epitaxial model. Agglomerated NiSi 2 particles were also observed in the NiSi 2 layer, and the density increased with increasing deposited Ni layer thickness. Lattice defects were generated in the Si epitaxial layer from the agglomerated NiSi 2 . Thus, the thinner the Ni deposited layer, the better the crystallinity of the Si epiaxial layer obtained.