The effect of end-of-range (EOR) dislocation loops on phosphorus diffusion was studied in the diffusion of P implanted in single-crystal and preamorphized silicon. After annealing at 850°C for 5 to 60 min in an oxidizating ambient, P profiles obtained by secondary-ion mass spectrometry (SIMS) showed that the transient enhanced diffusion of P is absent when the as-implanted phosphorus profile is located within the regrown amorphous layer. It was also found that EOR dislocation loops suppressed the oxidation-enhanced diffusion of phosphorus. It is proposed that the excess point defects generated during the oxidation and the annealing of implant damage were shielded by EOR dislocation loops acting as a diffusion barrier such that both the oxidation-enhanced diffusion and the transient enhancement in diffusivity were minimized.