This paper discusses the evolution in the degradation and breakdown behaviour of ultra-thin oxides when scaling the oxide thickness into the sub-4 nm range for future CMOS technology generations. It will be shown that changes in the breakdown statistics, which can be explained by a percolation model for breakdown, lead to an increased area dependence of the time-tobreakdown. This has to be taken into account when predicting the oxide reliability. Also the impact of the test methodology, the relevance of a so-called polarity gap in the charge-tobreakdown and its consequences for reliability testing, are highlighted. Moreover, a strong increase in the temperature dependence of breakdown, especially for sub-3 nm oxides, is demonstrated and the impact of temperature on trap generation and critical trap density at breakdown is discussed. Finally it is shown that the combined effects of all these phenomena might lead to oxide reliability becoming a potential showstopper for further technology scaling.