Al-Si contacts irradiated with arsenic ions and annealed at 200–500°C have been investigated for interfacial reactions and variations in electrical contact resistance. For arsenic doses above the amorphization threshold of silicon (about 2×1014 ions cm-2) the crystallographic reaction pits become irregular in shape and seem to be confined to the amorphous layer. The contact resistance on n+-Si is almost one order of magnitude higher in irradiated samples as compared with unirradiated samples after annealing at 425°C for 10 min. Nuclear reaction analysis indicates the presence of a thin interfacial oxide layer in Al-n+-Si samples. Differences in surface morphologies of ion-irradiated Al-n+-Si and Al-p+-Si samples after long-term annealing at 200°C suggest that the dispersion of the interfacial oxide is very limited for the ion doses used in this study.