Transient enhanced diffusion of implanted arsenic in silicon with/without additional self-implantation has been investigated. The experimental results show the suppression of As diffusion with Si self-implantation during initial stage of annealing in contrast to the prediction of conventional models. The results suggest that the arsenic and self-interstitial atoms might form immobile clusters during Si implantation or initial stage of annealing. After the clusters dissolve for further annealing, the transient enhanced diffusion of As increases with silicon implantation dose as expected from the “+1” model. These results clarify that interstitials/ As-I clusters play a major role in transient arsenic diffusion.