A high voltage GaAs heterojunction bipolar transistor (HBT) with an open-base collector breakdown voltage of 106 V and an open-emitter breakdown voltage of 134 V has been demonstrated. A vertical structure with a doped GaAs substrate, a 9.0 mum thick collector doped to 2.0 x 10(15) cm(-3), and a backside collector contact were used to achieve this breakdown. The same breakdown voltage results were measured for HBTs with very different emitter areas and geometries, and are consistent with bulk breakdown in GaAs. Devices with 4 x 40 mum(2) emitters show DC current gain of 38 at 6000 A/cm(2). The device rf performance was limited due to extrinsic pad capacitance to the substrate, with f(t) and f(max) values of 1.16 and 3.0 GHz, respectively. However, intrinsic f(t) of approximately 16 GHz can be achieved through the use of thicker dielectric insulation.