We have studied the nitrogen composition dependence of the characteristics of TaN/HfLaON/ $\hbox{Hf}_{1 - x - y}\hbox{N}_{x}\hbox{O}_{y}/\hbox{SiO}_{2}/\hbox{Si}$ MONOS memory devices. By increasing the N composition in the $ \hbox{Hf}_{1 - x - y}\hbox{N}_{x}\hbox{O}_{y}$ trapping layer, both the memory window and high-temperature retention improved. The $\hbox{Hf}_{0.3}\hbox{N}_{0.2} \hbox{O}_{0.5}$ MONOS device displayed good characteristics in terms of its $\pm$9-V program/erase (P/E) voltage, 100- $\mu\hbox{s}$ P/E speed, large initial 2.8-V memory window, and a ten-year extrapolated retention of 1.8 V at 85 $^{\circ}\hbox{C}$ or 1.5 V at 125 $^{\circ}\hbox{C}$ .