Disclosed is a method of manufacturing an integrated circuit comprising a bipolar transistor, the method comprising providing a substrate (10) comprising a pair of first isolation regions (12) separated from each other by an active region (11) comprising a collector impurity said bipolar transistor; forming a base layer stack (14, 14′) over said substrate; forming a further stack of a migration layer (15) having a first migration temperature and an etch stop layer (20) over said base layer stack (14); forming a base contact layer (16) having a second migration temperature over the further stack, the second migration temperature being higher than the first migration temperature; etching an emitter window (28) in the base contact layer over the active region, said etching step terminating at the etch stop layer; at least partially removing the etch stop layer, thereby forming cavities (29) extending from the emitter window in between the base contact layer and the redistribution layer; and exposing the resultant structure to the first migration temperature in a hydrogen atmosphere, thereby filling the cavities with the migration layer material. An IC comprising such a bipolar transistor is also disclosed.