Current‐voltage characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy with nonuniform doping in the base region have been studied. Experimental measurements indicate that an optimization of the base doping leads to substantial improvement in the current gain and related properties. Unequal variations of the band‐gap narrowing effect and Fermi–Dirac statistics effect seem to underlie this improvement. It is found that, in general, the higher the nonuniformity of the base doping, the lower is the offset voltage of the HBT.