The diffusion behavior of implanted arsenic in polycrystalline silicon was investigated, using backscattering and electrical measurements. The diffusion coefficient isD=8.5×10−3 exp (−2.74/kT) for polycrystalline silicon deposited on freshly-etched silicon andD=1.66 exp (−3.22/kT) for the deposition on silicon having natural oxide. At the interface to the single-crystalline silicon, a pile-up of arsenic occurs, which depends also on the surface treatment prior to the deposition of the polycrystalline silicon.