Abstract: SOI（Silicon On Insulator） material fabricated by SIMOX（Separation by Implantation of Oxygen） technology with co-implantation of hydrogen and oxygen.The effect of co-implantation of hydrogen and oxygen on the structure of BOX（Buried Oxide）layer which is a crucial part of SOI wereinvestigated. Comparing the microstructure of as-implanted wafer and annealed wafer by analyses of SIMS and XTEM, it is found that the implantation of hydrogen benefits to broaden the thickness of BOX layer.Further results show that the implantation at room temperature broadens BOX layer muchmore than at high temperature.