In this study we used transmission electron microscopy (TEM) to assess the origin of the electrical behaviour of two dimensional electron gas (2DEG) in high electron mobility transistors (HEMTs) based upon InAlAs/InGaAs heterostructures grown on InP substrates, as a function of the growth temperature (Tg) of the InxGa1 − xAs well. The highest mobility for a matched channel was obtained for an In0.53Ga0.47As layer grown at 530 °C. Lower temperatures reduced the mobility values and led to higher mobilities for [1̄10] due to the surface corrugation along [110], induced by lateral decomposition of the InGaAs at low growth temperatures.