Heterojunction bipolar transistors (HBTs) are becoming increasingly important for highspeed electronic applications. This paper will discuss how the unique growth chemistry of metalorganic molecular beam epitaxy (MOMBE) can be used to produce high performance HBTs. For example, it has been well documented that MOMBE's ability to grow heavily doped, well-confined layers of either n- or p-type is a significant advantage for this device. This feature arises primarily from the ability to use gaseous dopant sources in the absence of interfacial gas boundary layers. While this is an advantage for doping, it can be a disadvantage in other areas such as AlGaAs purity or InGaP lattice matching. This paper will discuss how these difficulties can be overcome through the use of novel Al or Ga precursors thus allowing deposition of high quality GaAs-based HBTs. By using trimethylamine alane (TMAA), background impurity concentrations can be reduced substantially. Further improvements in purity require cleaner Ga precursors or alternatively novel Ga substitutes. The resulting reduction in compensation allows for the use of lower dopant concentrations in the AlGaAs thus producing significant improvement in the leakage behavior of the base-emitter junction. Even further improvement can be achieved through the use of InGaP. Using novel Ga precursors, such as tri-isobutylgallium (TIBG), the problems associated with the sensitivity of composition to growth temperature are greatly reduced, allowing for the reproducible deposition of devices containing InGaP emitter layers.