We report on the thermal stability and trap characteristics of HfON as a trapping layer in charge trap flash memory device applications. Compared to HfO2, HfON prepared by NH3 annealing of HfO2 exhibits good interfacial quality, excellent memory properties, and superior thermal stability. The improvement in thermal stability can be explained by the lower interfacial reaction and amorphous state of HfON. The activation energy of a SiO2/HfON/Al2O3 device and the trap level of the HfON trapping layer were found to be 1.08 and 1.04 eV, respectively.