The split collector resistance is a specialized in-line Process Control Monitor (PCM) test used to determine the device performance in GaAs HBT processing. It is the resistance measured between two adjacent collector structures using a two point probe technique. This paper is motivated by the investigation of intermittent high split collector resistance detected in GaAs HBT manufacturing. The root cause analysis was focused on the major contributors to the collector metal module. Specifically, the collector metallization and the post collector alloy processes were investigated and optimized. Progress was achieved in both reducing the split collector resistance and the overall reliability of the device. This paper explores the areas examined and describes the improvements made to tighten the split collector resistance distribution.