Silicon-Germanium Heterojunction Bipolar Transistors (SiGe HBTs) are perfectly suited for high-speed electronics. Since the fabrication costs per design cycle are rapidly increasing with progressing frequency and complexity of the systems, accurate compact models are essential in order to enable robust circuit design. This thesis focuses on selected important physical effects in advanced SiGe HBTs, which have been either insufficiently modeled or completely missing in conventional compact models. New compact model equations for the transfer current were derived and successfully applied to a...