The thermal stability of nickel silicide (NiSi) on source/drain and gate is one of the important research topics in complementary metal oxide semiconductor technology. Here we report the effects of germanium-ion implantation (GeI/I) on the thermal stability of NiSi on poly-Si gates. Scanning electron microscope inspections and thin-film X-ray diffraction results show that agglomeration and NiSi2 transformation can be suppressed by high dosage Ge implanted on poly-Si gates. The allowable process temperature of NiSi formation can be increased by 100 degrees C.