The behaviour of 80 keV arsenic ions implanted at room temperature in oriented and disoriented silicon crystals below the amorphization dose, has been studied by measuring the physical profile and the electrical profile following isochronal anneals. From the analysis of the physical profile, the penetration parameters, [MATH]p, Ɗ[MATH]p, and Rmax for ions channeled along < 111 > axis, have been measured. After isochronal annealing of off-channeling implants, an effective diffusion coefficient at 900 °C for arsenic equal to 5 × 10-16 cm2· s-1 has been calculated. It is shown that for arsenic ions implanted in disoriented silicon, the electrically active fraction, which is about 0.4 after 30 min annealing at 600 °C increases continuously until 100 % electrical activation of the arsenic ions is reached at about 900 °C. Similar trend is observed for < 111 > channeled implants. The annealing process appears to follow a first order reaction kinetics with an activation energy equal to 0.4-0.5 eV. A tentative interpretation of the mechanism involved is given