The NiSi silicide that forms by reactive diffusion between Ni and Si active regions of nanotransistors is used nowadays as contacts in nanoelectronics because of its low resistivity. Pt is added to the Ni film in order to stabilise the NiSi phase against the formation of the high-resistivity NiSi2phase and agglomeration. In situ X-ray diffraction (XRD) experiments performed on material aged at 350 °C (under vacuum) showed the complete consumption of the Ni (5 at% Pt) phase, the regression of Ni2Si phase as well as the growth of the NiSi phase after 48 min. Pt distribution for this heat treatment has been analysed by laser-assisted tomographic atom probe (LATAP). An enrichment of platinum in the middle of the NiSi phase suggests that Pt is almost immobile during the growth of NiSi at the two interfaces: Ni2Si/NiSi and NiSi/Si. In the peak, platinum was found to substitute for Ni in the NiSi phase. Very small amounts of Pt were also found in the Ni2Si phase close to the surface and at the NiSi/Si interface. \textcopyright 2009 Elsevier B.V. All rights reserved.