NiSi is a promising material on salicide process. However, the thermal stability of NiSi is still a significant problem. Degradation in sheet resistance of Ni suicide is originated from phase transition from NiSi to NiSi2 and/or agglomeration of the suicide layers. We noticed the phenomenon that the sheet resistance increased irregularly at the temperature region for the phase transition, that is, the peak characteristics appeared in the transformation curve of sheet resistance. In this work, condition of generating the high resistance state was revealed by changing temperature, ramping rate and duration time in the silicidation process.