A theoretical treatment of the current transport in MSM devices is presented. It is based upon the application of the thermionic diffusion theory to both junctions and makes it possible to relate the current density to the total voltage applied to the device by a single expression valid for any voltage above reach through. So doing, the contributions of the different transport mechanisms, i.e., thermionic injection over the energy barriers at the junctions and drift diffusion within the semiconductor, may be evaluated both for majority and minority carriers. It turns out that before the flat‐band condition the current is limited by transport phenomena in the semiconductor, while above flat band neither mechanism definitely prevails. However, in spite of the different physical models, numerical results are of the same order of magnitude as those obtained by Szeet al.