Both AlxGa1−xAs/AlyGa1−yAs and GaAs pseudo-heterojunction bipolar transistors (HBTs) with lateral emitter resistors (laterally extended emitter ledge) are shown to exhibit base current ideality factors of 1.3 and 1.1, and uniform current gains of 10 and 5, respectively, even at current densities as low as 5×10−11 A/μm2. With this test structure, it is possible to separate the surface effects from the bulk effects. The structures investigated also allowed the confirmation that the emitter edge-thinning reported recently is very effective for reducing the surface recombination. The structures under investigation also show that GaAs HBTs can operate at collector currents in the microampere range or below.