The current-voltage characteristic of a long three-layer semiconductor diode of the type: p+−n−n+, p+−n−p+, n+−n−n+, etc. has been calculated. Expressions are obtained for the current-voltage characteristic of a three-layer semiconductor structure, the base of which is made of a compensated semiconductor, taking into account the strength of the external electric field. It is shown that due to the presence of zero, minus and plus charged impurities in a compensated semiconductor, the dependence of the concentration of electrons and holes is non-linear.