0.1 and 30 keV Si2+ focused ion beams (FIB) were implanted in two types of GaAs, one of which is semi-insulating (s.i.) GaAs, while the other is grown by molecular beam epitaxy (MBE). Successive regrowth over the implanted surface was performed using MBE-FIB combined system, and the resistance was measured. It was found that for 100 eV Si2+ FIB implantation, the sample was nonconductive without a post annealing at 800°C. After the post annealing, however, the sample became conductive, and the resistance was the same order in magnitude as the sample fabricated using 30 keV Si + FIB irradiation. This suggests a potential of selective formation of Si δ-like doped layers in GaAs and GaAs/AlGaAs using a low-energy FIB.