The degradations in NPN silicon-germanium(SiGe) heterojunction bipolar transistors(HBTs) were fully studied in this work, by means of 25-MeV Si, 10-MeV Cl, 20-MeV Br, and 10-MeV Br ion irradiation, respectively. Electrical parameters such as the base current(IB), current gain(β), neutral base recombination(NBR), and Early voltage(VA)were investigated and used to evaluate the tolerance to heavy ion irradiation. Experimental results demonstrate that device degradations are indeed radiation-source-dependent, and the larger the ion nuclear energy loss is, the more the displacement damages are, and thereby the more serious the performance degradation is. The maximum degradation was observed in the transistors irradiated by 10-MeV Br. For 20-MeV and 10-MeV Br ion irradiation, an unexpected degradation in ICwas observed and Early voltage decreased with increasing ion fluence, and NBR appeared to slow down at high ion fluence.The degradations in SiGe HBTs were mainly attributed to the displacement damages created by heavy ion irradiation in the transistors. The underlying physical mechanisms are analyzed and investigated in detail. The degradations in NPN silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) were fully studied in this work, by means of 25-MeV Si, 10- MeV Cl, 20- MeV Br, and 10- MeV Br ion irradiation, . Electrical parameters such as the base current (IB), current gain (β), neutral base recombination (NBR), and Early voltage (VA) were investigated and used to evaluate the tolerance to heavy ion irradiation. Experimental results demonstrate that device degradations are indeed radiation-source-dependent, and the larger the ion nuclear energy loss is, the more the displacement nuclear are loss, and more the displacement nuclear are loss, and the more serious the performance degradation is. For 20-MeV and 10-MeV Br ion irradiation, an unexpected degradation in ICwas observed and Early voltage decreased with increasing fluence, and NBR has been slow down at high ion fluence. Degradations in SiGe HBTs were mainly attributed to the displac ement damages created by heavy ion irradiation in the transistors. The underlying physical mechanisms are analyzed and investigated in detail.