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AlGaAs/GaAs single heterojunction bipolar transistor (HBT) structures with Be- and C-doped bases have been annealed at different temperatures using rapid thermal processing (RTP). Both electrical and low-temperature photoluminescence measurements were used to investigate their thermal stability. We found that the conventional AlGaAs/GaAs abrupt HBT structures could undergo significant degradation at temperatures commonly encountered in typical RTP for device fabrication. The decrease of current gain was observed in both molecular beam epitaxy-grown HBTs with a Be-doped base and metalorganic chemical vapor deposition-grown HBTs with a C-doped base after RTP at temperatures greater than 600 °C. Our studies show that high-temperature RTP could induce undesirable degradation in AlGaAs/GaAs HBTs. Different degradation mechanisms, which are similar to those for the degradation of the Be- and C-doped base HBTs under current-induced stress, are responsible for the degradation of the Be- and C-doped HBTs subjected to RTP. The degradation of Be-doped HBTs is believed to be due to the outdiffusion of Be from the highly doped base, whereas the decrease of current gain for C-doped HBTs is closely related to the unintentionally incorporated hydrogen during material growth. © 1999 American Institute of Physics.