Grown by molecular beam epitaxy, a sawtooth-doping-superlattice (SDS) structure has been employed in the collector region of a heterostructure-emitter bipolar transistor. For the studied structure, conventional transistor behavior and controllable S-shaped negative-differential-resistance (NDR) performance were simultaneously achieved. First, due to the avalanche multiplications within SDS periods or emitter-base p-n junction depletion region, a bi-directional switching phenomenon was exhibited under the two-terminal operation. In addition, when a base current or bias was applied, transistor properties and a controllable S-shaped NDR family in the large current regime were obtained. The best common-emitter current gain was 25. © 1993 Academic Press. All rights reserved.