We present a three-dimensional (3D) semi-classical ensemble Monte Carlo model newly developed to simulate a variety of nanoelectronic devices. The characteristics of the 3D model are compared with the widely used two-dimensional (2D) models. The advantages of our model, in terms of accuracy in modelling the physics behind the operation of nanodevices, are presented by applying it to T-branch junctions based on InGaAs/InAlAs heterostructures. Simulation of a T-branch junction with a Schottky gate terminal is presented, using both 2D and 3D models, demonstrating the necessity of using 3D simulation models to study the physics of complex-geometry nanostructures. Copyright © 2009 John Wiley & Sons, Ltd.