A novel and robust method to determine the internal variable base resistance (RB) of SiGe HBT from small‐signal S‐parameters measurement is developed in present work. The proposed method is adopted in two kinds of SiGe HBT compact models, MEXTRAM and HICUM. With the aid of auxiliary collector resistance, the lower and upper limits of RB are built up and a narrow variation range of RB is obtained. Thus, RB can be directly estimated from the small‐signal S‐parameters measurement. The proposed method is successfully applied to several sizes of SiGe HBTs and the experiment results shows that average error between the lower and upper limits of RB is less than 3% over a wide range of bias points, which can satisfy the demands of most engineering applications. Therefore, we believe that the proposed technique is a reliable routine applicable to estimate the base resistance in SiGe HBTs. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:555–560, 2017