The outdiffusion of Be implanted into GaAs has been found to be identical after capless or capped (Si3N4or SiO2) rapid thermal annealing (RTA) at 900–1000 °C and to depend on the Be dose and its proximity to the surface. The outdiffusion is more pronounced when the Be implant is shallow (<0.1 &mgr;m) and/or the Be+dose is high (>1×1015cm−2). It is demonstrated that the Be outdiffusion is driven by the presence of a highly damaged surface layer. Auger results suggest the formation of a BeOxcompound at the surface of a high‐dose (1×1016cm−2) Be‐implanted sample that underwent capless RTA at 1000 °C/1 s. It appears that BeOxformation occurs when the outdiffused Be interacts with the native Ga/As oxides during annealing. All the Be remaining in the GaAs after a >900 °C/2 s RTA is electrically active.