We have developed a novel technique for fabricating completely strain-relaxed SiGe-on-insulator substrates. It features melt solidification to solve the problems of high defect density and a rough surface concerning SiGe substrates for a strained-silicon complementary metal-oxide-semiconductor. The technique involves three main steps: (1) growth of a SiGe layer on a silicon-on-insulator, (SOI) substrate, (2) SiO2 capping to prevent germanium evaporation during annealing, and (3) melting and solidifying the SiGe layer accompanied with germanium diffusion into the SOI layer. The defect density of the fabricated substrate is less than 1000 cm(-2) and its surface roughness is 0.39 nm (rms).