Channeling‐effect measurements with MeV He ions have been used to study the lattice location of As in silicon. Over the concentration range studied (5 × 1019− 1.2 × 1021/cm3) As was found to be 90–95% on substitutional sites. However, it was found that bombardment with the analysis beam caused 20–40% of the As to move off lattice sites. This effect may be responsible for the relatively low As substitutional fraction found in previous investigations. No bombardment‐induced off‐lattice movement was found in Sb‐doped Si indicating that this movement is species dependent.