The grain boundary passivation effect in polycrystalline silicon (polysilicon) thin films by hydrogen implantation has been studied. Boron‐doped polysilicon was implanted with low‐energy ions followed by low‐temperature annealing. Resistivity measurements show that the change in resistivity after implantation depends on the boron concentration in polysilicon. At low boron concentration (<1×1019cm−3), three orders of magnitude decrease in resistivity has been achieved. However, at higher boron concentration (>1×1019cm−3), the resistivity increased after hydrogen implantation. This increase is ascribed to implant‐induced damage which cannot be totally recovered by low‐temperature annealing.