Rapid thermal annealing of arsenic implanted ⟨100⟩ silicon single crystals has been studied by Rutherford backscattering/channeling spectrometry, and Hall effect/resistivity measurements, combined with layer removal. Redistribution of the implanted arsenic was followed as a function of anneal time (6–60 s including temperature rise time) and implanted peak concentration (3–10×1020cm−3) at temperatures of 1050 and 1090 °C. The maximum concentration of electrically active arsenic was found to be 2–3×1020cm−3independent of anneal time and implanted peak concentration. Fast arsenic redistribution was observed to take place within the first 20 s of annealing. Complete arsenic activation occurred by means of rapid redistribution to the solubility limit.