This work reports on the impact of nitric oxide (NO) nitridation on physical and electrical properties of thin steam gate or tunnel oxides. The oxides (similar to 7 nm) have been annealed in NO ambient under different annealing times and NO fluxes, and for comparison in nitrous oxide (N2O). Nitridation causes nitrogen to pile up near the SiO2/Si interface, producing interface regions with quite different physical and chemical properties according to whether NO or N2O is used. Secondary ion mass spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy measurements, combined with etch-rate experiments, show that in the case of NO, nitrogen is built up very close to the interface with a remarkably higher peak (at a lower thermal budget than N2O) and a narrower distribution, whereas with N2O, nitrogen distribution is broadened with a lower peak slightly displaced from the interface. The different behavior under reoxidation of NO- and N2O-annealed samples confirms the results mentioned previously. Physical analysis shows that the nitrided region is divided into an N-rich region at the interface with predominant Si-N bonds and a transition region further from the interface with a lower N content and fewer silicon nitride bonds. The two regions depend on the annealing conditions: the higher exposure produces a bigger N-rich and a smaller transition region. Electrical characterization shows that NO nitridation improves the oxide resistance to electrical stress for substrate carrier injection. However, a strong NO treatment degrades the oxide robustness during gate injection. Furthermore, a correlation between positive and negative trapping with transition and N-rich regions is observed under substrate injection conditions. Finally, the role of NO nitridation as boron diffusion barrier in surface p-channel metal-oxide semiconductor field effect transistor devices was investigated, showing that the higher nitrogen amount at the SiO2/Si interface the lower the B concentration reaching the silicon substrate.