Negative bias temperature instability is investigated on TaN metal-gated HfSiO(N) p-type metal oxide semiconductor field effect transistors. A previously developed measurement technique that allows to distinguish between the recoverable and the permanent components of the V-th shift is employed. When applied to nitrided and nonnitrided stacks, it is found that the permanent component is at most weakly influenced by the nitridation, while the recoverable component is strongly enhanced in the nitrided stacks. The nitrogen-related defect, which is responsible of the recoverable component increase, is clearly observed in the stress induced leakage current spectrum. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3058740]