Germanium-on-insulator (GOI) is desired for high performance metal-oxide-semiconductor transistors and monolithically integrated optoelectronics. We demonstrate a promising approach to achieve single-crystal defect-free GOI by using lateral over-growth through SiO2 window. The dislocations due to the lattice mismatch are effectively terminated and reduced in SiO2 trench by selective area heteroepitaxy combined with hydrogen annealing. Low defect density of 4× 106 cm-2 and low surface roughness of 0.7 nm (root-mean-square) on GOI are confirmed by plan-view transmission electron microscopy and atomic force microscopy analysis. In addition, the excellent metal-semiconductor-metal diode electrical characteristics fabricated on this GOI confirm Ge crystal quality. The selectively grown GOI structure can provide the monolithic integration of SiGe based devices on a Si very large scale integration (VLSI) platform