Irradiation of ion implanted semiconductors with high po-wer laser pulse produces a crystallization of the damaged la-yer and a redistribution of the dopant atoms (1). Both pheno-mena were accounted in terms of a liquid formation during illumination (2). Processes occuring in solid phase are ruled out because of the low value of the extrapolated growth rate of the amorphous layer just below the melting point and the diffusion coefficient in the solid semiconductor. Time resolved reflectivity measurements (3) clearly indicate a sharp increase of the reflectivity associated to the for mation of a liquid layer as a consequence of the laser pulse. The formation of a liquid layer is in principle capable to ex plain the main features of laser annealing. The impurity re-distribution is governed not only by the high value of the diffusion coefficient in liquid Si (Den10-4 cm²/sec) but also by the distribution coefficient K. Three different behavi-ours have been observed (1): only profile broadening for impurities having a Ko value ranging from 0.1 to 1 (As, P, B, etc.);