The main aim of this work is to study electron scattering in imperfect semiconductor heterostruetures. The source of unintentional disorder is the interface roughness at the heterojunctions occurring during growth. In order to achieve this goal we solve numerically the two–dimensional Ben Daniel–Duke equation for the electron scattering problem. Our model assumes open boundary conditions along the growth direction and periodic ones parallel to the heterojunctions. We then compute the reflection and transmission matrices that govern channel mixing due to interface roughness scattering. The knowledge of the mixing matrices allow us to calculate the transmission coefficient in any heterostruc-ture made of wide gap semiconductors. As an example, we compute the transmission coefficient in resonant tunneling devices based on double-barrier structures.