The redistribution of implanted ions within GaAs/AlAs multilayer structures due to post-implantation furnace annealing is reported in this paper. The structures were grown by molecular beam epitaxy on GaAs substrates and implanted with either hydrogen or beryllium ions. After furnace annealing at temperatures up to 700 C, these samples were examined using secondary ion mass spectrometry. The measurements show that the hydrogen and the beryllium atoms redistribute with post-implantation annealing and that both species accumulate at the buffer layer/substrate interface. The concentration of atoms at this interface can exceed 1E19/cm-3 and may be related to the crystal imperfections arising during the inital stages of epitaxy. The significant redistribution of implanted ions may also alter the optoelectronics properties of multilayer semiconductor structures processed in this manner for laser applications.