F+co‐implantation at different doses and energies was performed into GaAs already implanted with Be+at high dose (1015cm−2) and low energy (20 keV), in order to reduce the beryllium diffusion during post‐implant annealing. The redistribution behavior of Be and associated electrical effects were studied by secondary‐ion mass spectrometry, transmission electron microscopy (TEM), Hall effect measurements, and current‐voltage profiling. Be outdiffusion was reduced by co‐implantation of F; more than 80% of the implanted Be was retained during rapid thermal annealing up to 850 °C. The dose and energy of the F implant strongly influenced Be electrical activation efficiency. High activation, up to 48.5%, was obtained when F was co‐implanted at high dose (1015cm−2) and low energy (10 keV). Hole profiles shown reduced electrical activation in the region where F and Be profiles overlapped and TEM studies indicated the formation of {111} coherent plates, possibly BeF2precipitates, in the same region. The reduction of Be outdiffusion in F co‐implanted samples led to high activation after annealing, and was believed to be due to chemical interaction between Be and F.