Rapid thermal annealing (RTA) (800–1000°C, 1–60 s) was performed on capless and silicon nitride (SixNy) capped GaAs samples implanted with Si (30 keV, 4.5×1013cm−2 ) and SiF+ (50 keV, 4.5×1013cm−2 ). The maximum activation for the Si+ implants saturated at 25% (capless) and 42% (capped) and that for the SiF+ implants saturated at 20% (capless) and 35% (capped). The activation degraded at temperatures > 825°C due to surface decomposition in the capless annealing case and at > 925°C due to the cap failure in the capped annealing case. For all the RTA conditions studied here, higher activation always occurred with the Si+ rather SiF+ implants. An activation energy of 0.48 eV for the annealing process was determined from the electrical data. It was also observed that the heating and/or cooling rates can significantly influence the electrical activation.