Monte Carlo simulation of two-dimensional hot-electron gas in an InGaAs/InAlAs single heterostructure was carried out in order to clarify high-field drift velocity and drift velocity overshoot at 77 K. The electronic states of the two-dimensional electron gas are calculated self-consistently and are used to calculate the scattering probabilities. The importance of the conduction band nonparabolicity is shown by using the energy-band structures calculated by the k*p perturbation method for In/sub 0.53/Ga/sub 0.47/As and In/sub 0.52/Al/sub 0.48/As. In the present calculations alloy disorder scattering and two modes of LO phonons in InGaAs layers are taken into account in addition to acoustic deformation potential scattering, screened ionized impurity scattering, nonpolar optical phonon scattering, and intervalley phonon scattering. It is found that alloy disorder scattering reduces the drift velocity and that the maximum drift velocity and negative differential mobility depend on the energy separation between the Gamma and L valleys, indicating that the intervalley scattering plays an important role in hot-carrier transport in InGaAs/InAlAs single heterostructures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>