A method is provided for fabricating a semiconductor device and more particularly to a method of manufacturing a semiconductor device having radiation hardened buried insulators and isolation insulators in SOI technology. The method includes removing a substrate from an SOI wafer and selectively removing a buried oxide layer formed as a layer between the SOI wafer and active regions of a device. The method further comprises selectively removing isolation oxide formed between the active regions, and replacing the removed buried oxide layer and the isolation oxide with radiation hardened insulators.