We propose phosphorus (P) co-implantation as a simple and effective method for suppression of arsenic (As) loss from a junction formed by As implantation into a CoSi 2 layer and drive-in annealing. With this method, the reverse leakage current of the n + /p junction is lowered by more than two orders of magnitude without increasing the junction depth. By comparing P and Si co-implantation, we find that the suppressed dopant loss by P co-implantation can be attributed to the chemical species effect of P rather than an increased damage/amorphization by P co-implantation.