The quality of thin gate oxides grown on separation-by-implantation-of-oxygen silicon-on-insulator (SIMOX SOI) was investigated. The early-failure-rate of gate oxides in optimized SIMOX SOI has been as low as in bulk reference samples. Samples with low oxygen dose (4 x 10(17)/cm(2)) and relatively slow (1 degrees C/min) postimplantation anneal ramp up rate exhibited the best gate oxides. Surface roughness (up to 1 nm with 20 x 20 mu m scanned area) and SOI film thickness (150-230 nm) showed almost no impact on the early failure rate of the gate oxides on SIMOX SOI.