Dual passivation (with ledge structure and sulfur treatment) on base surface is employed to improve device performance of an InGaP/GaAs heterojunction bipolar transistor (HBT). By using this dual-passivation technique, good transistor characteristics such as dc current gain beta(F), offset voltage Delta V-CE, specific contact resistance pc, and sheet resistance R-sh are obtained. In addition, the InGaP/GaAs HBT with dual passivation exhibits improved thermal stability and microwave characteristics. Our experimental results suggest that the dual-passivated device can be used for high-temperature and/or low-power electronics applications. (c) 2007 American Vacuum Society.