In this paper we study the amount of electron quasi-Fermi level splitting in the emitter–base junction of single and double heterojunction bipolar transistors using a new numerical model that includes Fermi–Dirac statistics and base recombination current. The degree of splitting is different using our model than with previous models when high voltage or high doping levels are used. In order to illustrate its features, the model is applied to the study of collector current HBTs and DHBTs.