We report on the effect of external strain on the two-dimensional electron gas density in AlGaN/GaN heterostructures grown on sapphire by low pressure metalorganic chemical vapor deposition. The electron sheet concentration in the studied samples was4×1012–2×1013 cm−2and decreased with compressive strain. Lower doped heterostructures had a higher sensitivity to applied strain. The comparison between the experimental data and our model shows that the GaN layers are primarily nitrogen terminated at the heterointerface. ©1998 American Institute of Physics.