In this paper, the reactive ion etching (RIE) of Si1-xGex alloys using hydrogen bromide (HBr) plasma is reported. In order to obtain a more precise process control, the Ge content-dependence of HBr-basrd RIE etch rates has been studied. The experimental results showed that the RIE etch rate of SiGe increased monotonically with increasing the Ge-content in SiGe. The higher the Ge-content, the higher is the ratio of SiGe etch rate to Si etch rate. For instance, when x = 0.1, the ratio is 1.12, but, when x = 0.23, the ratio is 1.8. The HBr-based RIE process has been applied to the device fabrication of SiGe-heterojunction bipolar transistors (HBTs). Expected DC and high-frequency characteristics of processed SiGe HBTs have been obtained.