The characterization of the crystallinity by Raman image measurements has been made on thin silicon films on insulators, which are deposited by low pressure chemical vapor deposition using silane (SiH4) and disilane (Si2H6) as gas sources and are subsequently thermally annealed. The degree of crystallization by thermal annealing has been quantitatively evaluated by comparing the integrated Raman scattering intensity of the polycrystalline band and the amorphous band. The volume fraction of the crystalline component in samples grown with silane is larger than that grown with disilane for the same annealing time. Raman images of these thin silicon films reveal that the grain size in samples grown with disilane is a few microns, being bigger than that grown with silane. The affect of the source gas on the grain size of crystallites and on the volume fraction of the crystalline component in the films is attributed to the difference in nucleation rate for two kinds of the films during annealing. ©1995 American Institute of Physics.