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International audience; A Monte Carlo method is proposed for the study of in-plane electron transport in narrow gap heterostructures. Special attention is paid to the consequences of the strong nonparabolicity of the conduction band. The electron states are calculated within the framework of envelope function theory, which leads to a Schrödinger equation with an energy-dependent effective mass. This equation is solved in a numerically efficient way by including a standard eigenvalue solver in an iterative method. The mixing between conduction and valence band states is taken into account, at an approximate level, through a “Bloch overlap factor,” defined by analogy with the case of three-dimensional transport. This model was applied to a typical AlSb/InAs single well structure, and realistic results were obtained. The important role played by the Bloch overlap factor is demonstrated. When it is neglected, the mobility is strongly underestimated. A more sophisticated double well structure was also investigated. It is intended to reduce impact ionization, thanks to transfer toward the thinner well. This transfer is found to depend strongly on the potential profile