We have investigated the redistribution of implanted As during Ni 2Si formation at 275 and 300°C and NiSi formation at 400 to 700°C with neutron activation analysis and Hall effect measurement. Some of the implanted As atoms were found to redistribute themselves near the silicide-Si interface during both Ni2Si and NiSi formation. The depth of the redistribution extends about 100 Å into Si and is affected slightly by the formation temperature of NiSi. A fraction of the redistributed As is electrically active and the fraction increases with the annealing temperature. The maximum electrical activity of redistributed As during NiSi formation at 700°C is estimated to be 6.5%.