In this work we investigate the effect of nitridation on HfSiO's degradation under positive constant voltage stress. A comparison between decoupled plasma nitridation, annealing in NH3 and no nitridation is made. Stress induced leakage current dominates a wear-out phase before the final hard breakdown, regardless of nitridation. However, this progressive breakdown phase is more pronounced in NH3 annealed samples resulting in 60 times gate current increase after 10 years, 3 times higher compared to decoupled plasma nitridation and no nitridation. On the other hand, a shorter wear out phase is responsible for faster breakdown in plasma nitrided samples.