Raman spectra were recorded in backscattering from (100) oriented, Cr-doped, semi-insulating crystalline wafers of GaAs to characterize the changes introduced by implan-tation and by encapsulation and thermal anneal15ing. The studies were carried out at 300 and 100K. Implant fluences of lx1012 to 1x1015 S-ions/cm2 at 120 keV were used. Annealing temperatures ranged from 750 to 950°C for 15 minutes. The encapsulation was by means of rf-plasma-deposited Si3N4 films. The characteristics of a fixed annealing pro-cedure as a function of fluence and a fixed fluence at different annealing temperatures were determined. Unprocessed samples and a laser-annealed sample were studied. A pulsed, doubled YAG laser at 532 nm was used with about 16 mW of incident power in a 0.12-mm-diameter spot. A "triple" spectrometer, gated photon counting and computer pro-cessing of data were used. Following are the results: (1) the intensity of the LO pho-non line strongly varied with both implant dosage and annealing including a five-fold enhancement at 1012 S-ions/cm2 fluence, (2) the LO mode "softened" apparently due to implant-induced bond weakening, (3) polycrystalline and amorphous conditions of the implanted layer were identified, (4) thermal annealing itself was found to introduce disorder in the surface, at least for temperatures above 850°C, and (5) removal of amor-phous regions by laser annealing was observed.