The ambipolar mobility of charge carriers is discussed for compensated semiconductors with deep single-level traps; its influence on the double injection current is theoretically investigated. The I–U curve of a long sample is considered under the simultaneous variation of the ambipolar mobility and of the lifetime. Results are given for a strong equilibrium filling of the traps. Various mechanisms are considered of the formation of the stationary spatial distribution of the carriers assuming a weak variation of the lifetime. Conditions are studied under which the negative resistance arises due to the rise of the ambipolar mobility. [Russian Text Ignored.]