Selective-area epitaxy of carbon-doped (Al)GaAs by chemical beam epitaxy (CBE) on (100) GaAs substrates patterned with SiO2 has been studied. Triethylgallium, trimethylaluminum, tris-dimethylaminoarsenic (TDMAAs) and diiodomethane were used as precursors. True selectivity of GaAs and AlGaAs with a growth rate of 0.5 μm/h is achieved at a growth temperature as low as 470°C. A flat GaAs regrown surface can be obtained, however, only by thermally cracking the TDMAAs source at 350°C. The growth rate of GaAs:C layers is independent of the stripe openings down to about 5 μm. A growth rate enhancement is observed when the feature size is less than 5 μm. The “rabbit ear” thickness can be significantly reduced if the stripe opening is less than 5 μm or if theV/III incorporation ratio is low. A heterojunction bipolar transistor (HBT) with selectively regrown GaAs/AlGaAs:C external base layers has been successfully fabricated. It exhibits at least a 60% improvement in the base sheet resistance compared to the original HBT structure, demonstrating the potential of selective-area growth by CBE.