Defect states of hydrogenated amorphous silicon nitride (a-SiNx:H) thin films were measured using the thermally stimulated exoelectron emission spectroscopic method. The defect states of films with nitrogen to silicon composition ratios (x) of 0.92,121, and 1.44 were found to be located 1.66, 1.77, and 1.82 eV below the conduction band minimum, respectively. We confirmed that the hydrogen concentration decreased as x was increased via an elastic recoil detection analysis experiment, while as the hydrogen concentration increased, the defect concentration decreased. From these results, we concluded that the defect centers could be related to dangling bonds, the so-called K centers, in silicon nitride. Furthermore, as the concentration of Si H was increased with decreasing x via the infrared spectroscopy, the defect density was reduced through the defect passivation. (C) 2016 Elsevier B.V. All rights reserved.