Cathodoluminescence (CL) performed at low temperature has been used for the characterization of the fabrication technology of circuits implemented with heterojunction bipolar transistors. The cathodoluminescence signal from each GaAs layer has been identified. Different ion implantation masks, which protect the structure and the integrated resistors during the ion‐implantation step used for device insulation, have been investigated. Thin bilayers have to be used for the fabrication of the integrated resistors to obtain uniformity adequate for integrated circuits operation. Thicker bilayers are necessary in order to achieve an effective protection of the bottom and top layers of the mesa. CL results have been compared with electrical measurements showing a very good correlation. Its ability to obtain different penetration depths and to perform CL images as well as secondary‐ or backscattered‐electron images makes of the CL technique a powerful microcharacterization method.