The electrostatic discharge (ESD) characteristics of the pn junction diodes with different configurations in a silicon-germanium heterojunction bipolar transistor (SiGe HBT) based on a 0.18 /spl mu/m SiGe BiCMOS process is investigated. From the measured results, for the thin-base SiGe HBT, the base-collector junction diode shows the best ESD performance among all kinds of diode configurations owing to its large junction area.