The thermal stability of silicide on polycrystalline Si (poly-Si) has been investigated. At elevated temperatures, the silicide/poly-Si layered structure becomes morphologically unstable, because of the grain growth of poly-Si. The driving force for the high temperature instability is the reduction of the grain boundary energy and surface energy of the poly-Si. In situ stress measurement shows that the grain growth is accompanied by a decrease in the compressive stress of as-deposited poly-Si. A change in crystallographic texture from (110) to (111) is also observed during the grain growth, indicating a process similar to that of secondary grain growth. A study of the grain growth kinetics shows that the grain growth of poly-Si is enhanced by fast diffusion in the silicide, but is not rate limited by the diffusion of the dominant diffusion species in the silicide. A strong correlation is found between the onset temperature for plastic deformation in the silicide and that of the grain growth in poly-Si.