The effect of film thickness on the NiSi-to-NiSi2 transition temperature in the Ni/Pt/Si(100) system has been studied. Three sets of Ni/Pt/Si(100) bilayered samples with the same Ni:Pt ratios but with different film thicknesses were annealed by rapid thermal annealing at 750–900 °C. Both the x-ray diffraction analysis and the sheet resistance measurement show that the thermal stability of Ni(Pt)Si films improves with a decrease in film thickness. This property of Ni(Pt)Si films reveals the good potential for its applications in ultrashallow junctions. The experimental results are explained in terms of classical nucleation theory. © 2002 American Institute of Physics.