A heterojunction bipolar transistor (HBT) is fabricated using a selectively implanted collector (SIC) implant mask including multiple openings located over the HBT's collector region. During the SIC implant process, resist mask edge (well proximity) effects caused by the SIC dopant passing through the multiple openings generates multiple secondary shallow increased-doping regions in the collector region adjacent to the substrate surface, where the mask openings are sized such that each secondary increased-doping region has a doping concentration that is comparable to primary increased-doping regions, which are simultaneously formed deeper in the SIC region. A base structure and an emitter structure are then formed over the SIC region using known techniques. The secondary increased-doping regions produce enhanced base-collector junction between the SIC region and the base structure that measurably decreases Kirk Effect by way of enhancing the HBT's cutoff frequency (Ft) and break-down voltage (BVCEO).