A grain‐growth study of polycrystalline silicon having small dendritic crystallites obtained by cracking SiHCl3on a hot filament has been carried out in the temperature range 1275–1375 °C. It has been observed that (1) the grain growth in the polycrystalline silicon is due to a two‐dimensional motion of grain boundaries in a plane perpendicular to the grain axis, (2) the size‐limited grain‐growth law is obeyed, and (3) the activation energy of grain growth in polycrystalline silicon is 4.62±0.23 eV, which is nearly the same as the activation energy of the diffusion of Si31in silicon.