Stationary distributions of the field and the electron density of the trapped domain in highly doped Gunn devices are calculated by a computer simulation and a simple numerical analysis. From these results, characteristics of the bistable switching due to the static negative resistance are clarified against the donor density of the active region. The results of the computer simulation also demonstrates possibilities of the wide band reflection amplification with the frequencies independent of the transit time in the overcritically doped Gunn diodes.