The NiSi silicide that forms by reactive diffusion between Ni and Si-rich active regions of nanotransistors is currently used for contacts in nanoelectronics because of its low resistivity. The redistribution of boron during reactive diffusion between Ni (30 nm) and B doped-Si has been investigated by laser assisted wide-angle tomographic atom probe (LAWATAP). Two states were characterized (room temperature and rapid thermal annealing at 450 °C for 1 min). LAWATAP shows that after deposition of Ni (30 nm) at room temperature a very thin film (7 nm) of Ni silicide was formed. The initial boron distribution in silicon is almost unchanged. After a heat treatment in vacuum at 450 °C (1 min) the nickel monosilicide NiSi was formed. Boron distribution at this stage is very different from that at room temperature. Boron is shown to accumulate at NiSi/Si interface due to snowplow effect. Very small amounts of boron were also found in NiSi phase close to the surface. Crown Copyright \textcopyright 2009.