Abstract: SIMON（Separated by Implanting Oxygen and Nitrogen）wafers were fabricated with oxygen and nitrogen co-implantation.The structure of samples were studied by secondary ions mass spec-troscopy（SIMS）and by cross-sectional transmission electron microscopy（XTEM）analysis.The relationship between radiation hardnessproperties and the status of buried layersin SIMON wafers were investigated.The results show that the buried layer is better for the wafer with lower nitrogen implanta-tion dose than for that with higher ni trogen implantation dose,and the ra diation hardnessproperties closely depend on the characteristic of the buried layer.The results also approve that the insulating ability of the buried layer of the wafersisone of the key factors affecting the hardening for SOI devices.