The operation of planar doped barrier diodes is studied using a numerical device simulation which solves the carrier energy transport equation self‐consistently with the current continuity equation and Poisson’s equation. This allows the effects of space‐charge injection and carrier heating, which have been neglected in previous studies of these devices, to be studied quantitatively. Results for two different doping profiles are presented and compared with the results calculated using the conventional quasi‐equilibrium transport model. Significant differences between the results are found, demonstrating the importance of including hot‐carrier effects in modeling these devices.