Application of implantation was demonstrated to be an effective method of mechanical stress relaxation in SOS structures. Experimental results were obtained concerning stress relaxation in SOS structures under post-implantation thermal treatments. Proposed models of defect formation and reconstruction near the Si-Al2O3 interface in conditions of high non-equilibrium concentration of point defects and impurities are discussed. The stress relaxation is explained by interaction of vacancy defects with compressive stresses and the probable creation of a dislocation not in the case of annealing after boron implantation. Theoretical consideration of stress distribution in SOS structures with compensating defects is presented. Evidence of accumulation of vacancy defects at the Si-Al2O3 interface was experimentally obtained and theoretically proved.