There exists a strong correlation between the nitrogen concentration profile and infrared (IR) spectroscopy in gate oxynitrides for metal–oxide–Si (MOS) devices. The hot-electron hardness of the MOS device depends strongly on the nitrogen concentration profile in the gate oxide. It is experimentally found that the concentration ratios of nitrogen atSiO2/Sito the maximum amount of nitrogen in the oxide bulk([N]int./[N]max. bulk)are proportional to the values of IR peak positions of Si–O stretching bonds. A larger value of[N]int./[N]max. bulkindicates a better hot-electron hardness of the MOS device, which can be explained by a reduction ofSiO2/Siinterfacial strain. The hot-electron hardness in the MOS device can be easily assessed by the IR signals of gate oxynitrides. ©1998 American Institute of Physics.