This paper deals with the problem of ohmic contacts modeling for Monte Carlo simulation of high electron mobility transistors (HEMT). As it is practically impossible to simulate ohmic contacts, they are replaced by boundary conditions (BC). The simulated behaviour of devices is strongly influenced by BC, especially in the case of submicron gate lengths. Standard models prescribe a neutrally charged region and are inconsistent with the presence of heterojunctions. This may lead to dramatically unphysical effects. An alternative is proposed where an equilibrium density profile is self-consistently calculated and serves as BC. The comparison of our new model with the former one has been performed and we have used experimental structures to optimise the model parameters. (C) 2003 Elsevier Ltd. All rights reserved.