The interactions, in GaAlAs/GaAs heterojunction bipolar transistor structures, between implanted Mg atoms and differentp‐type base dopants (Be in layers grown by molecular beam epitaxy, Zn or C in layers grown by organometallic chemical vapor deposition) have been investigated. Different diffusion behaviors have been observed, according to the base dopant, either for the implanted Mg or for the base dopant itself. The resultant hole concentration profile obtained with aC–Velectrochemical profiler has also been studied as a function of the basep‐type dopant.