The morphological stability of TiSi2 in Ti/polycrystalline Si (poly-Si) and Ti/amorphous silicon (a-Si) samples has been investigated by both cross-section and planview transmission electron microscopy as well as by sheet resistance measurement. The agglomeration of TiSi2, in Ti/poly-Si samples was found to occur after annealing at 800 degrees C for 1 h. In contrast, almost full surface coverage of TiSi2 grains was observed on originally a-Si substrate at 900 degrees C for I h. The results indicated that the reaction of Ti thin films with a-Si results in the formation of fine TiSi2 grains which in turn enhances the morphological stability of TiSi2. Sheet resistance data were found to correlate well with the morphological and microstructural observation.