The recently reported post-stress degradation of MOSFETs is investigated in more detail in this paper. The interface trap generation post hole injection is found to be two orders of magnitude slower than that post-irradiation and cannot be satisfactorily explained by the transportation of hydrogen species across the bulk of oxide. There is a lack of correlation between the trapped hole removal and the interface trap creation, which is against the prediction of the trapped hole conversion model. It is found that the interface traps generated during and post the stress originate from two different defects. The defect responsible for the post-stress generation is excited by the hole injection and then converted into an interface trap if a positive gate bias is applied post-stress.