We have studied As clustering and oxidation of As-implanted Si after a preoxidation (ramp-up) period with (N-2 + 1% O-2) ambients. Sheet resistance measurements along with channeling studies indicate that significant arsenic clustering and arsenic supersaturation in Si occurred after ramping periods at 750 degrees C and 850 degrees C compared with results at 950 degrees C and 1050 degrees C. For very high As implantation fluences, the arsenic supersaturation with cluster formation near the silicon surface produced a higher oxidation rate at 750 degrees C and 850 degrees C than at 950 degrees C.