The quality of thin gate oxides grown on separation by implantation of oxygen substrates was examined. The basic mechanisms for time dependent breakdown were shown to be the same as oxides grown on bulk substrates, while detailed I-V characteristics of the gate oxide indicates that there can be more oxide trapped charges, most likely caused by the material defects of silicon on insulator wafers, that do not significantly reduce the charge-to-breakdown (Q(bd)) value. However, by examining the early-failure-rate, the catastrophic gate oxide defect density can be deduced. A similar study was also performed to evaluate the buried oxide quality.