The energy barrier between the metal Fermi level and the insulator conduction band is directly determined using internal electron photoemission at the interfaces of metallic, nitrides (TiNx, TaNx) with SiO2 and HfO2. TiNx yields high barriers both on SiO2(4.15 +/- 0.05eV) and HfO2 (3.0 +/- 0.05 eV) stable upon annealing at temperatures up to 1000 degrees C. Incorporation of a monolayer HfO2 at the TiNx/SiO2 interface causes approximate to 0.2 eV barrier enhancement upon annealing. The TaNx/SiO2 interface barrier (3.55 0.05 eV) is found to be stable under annealing up to 1000 degrees C, but Hf contamination leads to a barrier increase similar to that observed for TiNx/SiO2. The as-deposited TaNx on HfO2 yields a low barrier (2.1 +/- 0.05 eV), but it significantly increases upon annealing, suggesting a chemical interaction to occur between TaNx and HfO2. (c) 2005 American Institute of Physics.