High leakage currents at the base-collector junction of heterojunction bipolar transistors have been mentioned by several authors. In this article, we compare two pre-epitaxy cleaning procedures which both allow smooth epitaxy without any extended defects. Using our initial cleaning procedure, we obtained leakage current values in the range of the published results. We show that our results were consistent with the presence of defects induced by the low-energy reactive ion etching involved in this procedure. In contrast, we obtain a very significant reduction of the leakage current using our new all-wet chemical cleaning.