A thermal impedance model of single-finger and multi-finger SiGe heterojunction bipolar transistors (HBTs) is presented. The heat flow analysis through the device has to be considered in two diffusion parts: the front-end-of-line (FEOL) diffusion and the back-end-of-line (BEOL) diffusion. Therefore, this new thermal impedance model features multi-poles network which has been incorporated in HiCuM L2 compact model. The HiCuM compact model simulation results are compared with on-wafer low-frequency S-parameters measurements at room temperature highlighting the device frequency dependence of self-heating mechanism. The simulation results are also compared to pulse measurements to improve reliability analysis.