Much of the technology of our era is based on the SiO2/Si amorphous/crystalline heterojunction interface. Now it appears that As2S3/GaAs amorphous/crystalline heterojunctions show some technological promise. We have found that properly prepared As2S3/GaAs interfaces can have reasonably good electronic quality. The interfacial recombination velocity is ≊15 000 cm/s at flat band, which results in a ∼100‐fold reduction of perimeter recombination currents inp‐njunction mesas. This can be important on heterojunction transistor emitter‐base perimeters, solar cell and light‐emitting diode perimeters, and for reducing mirror facet recombination in semiconductor lasers.