The formation of Ni silicides on (001)Si with a thin interposing Pt layer has been investigated. NiSi was observed to be the only silicide phase for the samples annealed at 500-800 degrees C with a thin interposing Pt layer. The sheet resistance maintained the same low level in a wide temperature range. Pt addition was found to retard significantly the formation of nickel silicides and enhance the thermal stability of NiSi thin films on (001)Si. For Ni(30 nm)/Pt(1.5 nm)/(001)Si, the process window of NiSi was extended to 500-800 degrees C. The effects of a thin interposing Pt layer on the formation of Ni silicides on (001)Si are discussed.