The oxidation-induced Ge condensation process of SiGe/Si on insulator structures has been investigated. The relaxation rate obtained in the SiGe layers on insulator (SGOI) abruptly decreased with decreasing SGOT thickness below 50 nm. In order to enhance the relaxation rate in the ultra-thin SGOI, the new technique combined with H+ irradiation with a medium dose (5 x 10(15) cm(-2)) and post-annealing (1200 degrees C) has been developed. It was demonstrated that the highly relaxed (70%) ultra-thin SGOI with a low defect density (8 x 10(6) cm(-2)) has been realized by this technique. (c) 2005 Elsevier B.V. All rights reserved.