An analytical solution for the minority carrier concentration in the base region of an emitter–base–emitter contact topology heterojunction bipolar transistor has been developed. This solution is used to calculate various base current components, including the mesa surface recombination current which is geometry dependent. This mesa surface recombination current affects the efficiency with which the injected carriers from emitter traverse the base and reach the collector. The significance of this mesa surface recombination current is evaluated and the current gain is calculated as a function of device geometry and base doping level. In particular, the effect of this mesa surface recombination is examined for devices specifically designed for high frequency applications. The emitter crowding is also analyzed quantitatively and its effects on device current gain are discussed.