A recently developed As2S3chemical treatment was used to passivate the perimeters of self‐aligned heterojunction bipolar transistors (HBTs). The As2S3chemical treatment significantly lowered the base current resulting in a two order of magnitude reduction in the collector current density at which dc current gain was observed (&bgr;=1). No degradation with time has been observed in the electrical characteristics of the chemically treated HBTs. This absence of degradation is attributed to the impermeability to oxygen of the As2S3glass which coats the perimeter of the HBT after chemical treatment.