Results of a large-signal RF reliability study of SiGe HBTs are presented. The study consists of consecutive stress phases with different stress conditions. First, the DUT is stressed statically, which leads only to the widely reported excess base current at relatively low injection levels. Second, the DUT is stressed dynamically with voltage swings that significantly exceed the statically defined open-base collector-emitter breakdown voltage. The DUT withstands this type of stress, which proves SiGe HBTs to be extremely robust. Third, experimental evidence is established for significant degradation of the admittance parameters that occurs only under extreme nonlinear large-signal operation. Further experimental evidence suggests that the observed degradation occurs inside the internal HBT.