This study delves deeper into the highfrequency behavior of state-of-the-art sub-THz silicongermanium heterojunction bipolar transistors (SiGe HBTs) fabricated with 55 nm BiCMOS process technology from STMicroelectronics. Using measurement data, calibrated TCAD simulations, and compact model simulations, we present a comprehensive methodology for extracting several high-frequency parameters (related to parasitic capacitance partitioning and non-quasi-static effects) of the industry standard model, HICUM. The parameter extraction strategies involve thorough physics-based investigation and sensitivity analysis. The latter allowed us to precisely evaluate the effects of parameter variations on frequencydependent characteristics. The accuracy of the finally deployed model is tested by comparing the model simulation with measured small-signal two-port parameters of SiGe HBTs up to 330 GHz.