Rapid thermal processing as a post‐oxidation annealing (POA) process is of considerable influence on the quality of thin thermal oxides: The number of defect‐related oxide failures is reduced, together with a slight reduction of the intrinsic oxide quality, but to a degree that is of no importance as regards reliability aspects. According to our investigations, it is important that POA is performed after poly‐Si deposition and doping, whereas POA after poly‐Si patterning is found to be an undesirable process. Infrared spectroscopy indicates stress relaxation caused by the POA treatment, but no change of the SiO2/Si‐interface roughness could be observed by high‐resolution electron microscopy. This relaxation process was accompanied by the creation of electron traps. Constant‐current investigations indicated an enhanced electron trapping in the oxides after POA. This electron trapping increased with increasing POA temperature. The reduced defect‐related oxide failures after POA are attributed to a retarded runaway of the injection current by negative space charges.