N-type, 1015 −1016 cm−3 doped, Fz, Silicon has been implanted with 1 to 4 × 1012 cm−2, 100 or 300 keV, As ions. The nature and concentration of the defects has been monitored using Deep Level transient Spectroscopy as a function of the thermal treatment (in the range 500–900°C) and of the energy of the pulse (15 ns) of a ruby (0.69,μm) laser (in the range 0.3 to 0.6 J cm−2). The defects resulting from annealing by the two treatments are found to be the same. Only, for energies higher than 0.5 J cm−2, the laser treatment introduced new defects (at Ec−0. 32 eV), presumably resulting from a quenching process. Thus a laser energy below the theshold for melting and epitaxial recrystallization is able to anneal the defects produced by implantation, demonstrating that the annealing process induced by the laser pulse is not a purely thermal process but probably involves an ionization enhanced mechanism.