The probability of finding In–N and N–N closely spaced pairs in In x Ga 1− x As 1− y N y∕ Ga As quasi-lattice-matched quantum wells (x= 0.13, y= 0.045) has been measured by cross-sectional scanning tunneling microscopy. The average number of In–N bonds is higher than expected for a random distribution in both as-grown and annealed samples, but lower than that predicted by current theoretical calculations. Our measurements show no N outdiffusion and little change in the spatial distribution of In atoms as a result of annealing. However, a remarkable decrease in the number of N–N nearest neighbors and associated localized states is observed in annealed quantum wells.