Disclosed are embodiments of a transistor (e.g., bipolar junction transistor (BJT) or a heterojunction bipolar transistor (HBT)) and a method of forming the transistor with a collector region having a protected upper edge portion for reduced base-collector junction capacitance Cbc. In the embodiments, a collector region is positioned laterally adjacent to a trench isolation region within a substrate. Mask layer(s) cover the trench isolation region and further extend laterally onto the edge portion of the collector region. A first section of an intrinsic base layer is positioned above a center portion of the collector region and a second section of the intrinsic base layer is positioned above the mask layer(s). During processing these mask layer(s) prevent divot formation in the upper corner of the trench isolation region at the isolation region-collector region interface and further limit dopant diffusion from a subsequently formed raised extrinsic base layer into the collector region.