A heterojunction bipolar transistor is fabricated by laminating and emitter layer, a base layer and a collector layer on a top surface of a semiconductor substrate, forming a via hole through the emitter layer, the base layer, the collector layer and the substrate at a specific depth, and providing a heat sink layer made of a metal on a rear surface of the substrate. This marking technique is useful in tracking pirated data andor sources, such as CDs or DVDs, to thereby prevent future pirating of data. The portions are removed from the composite image of the collaborative session content.