AlGaAs/GaAs single HBTs from two different epi-layers with similar layer design, but with some variations in layer properties due to the particular features of individual epitaxial growth techniques, were simultaneously fabricated using a self-aligned process. These HBTs were tested for their reliability characteristics as well as their material quality using photo-luminescence and transmission electron microscopy. HBTs from one epi-layer showed high reliability characteristics and presented smaller carrier recombination lifetime (tau(B) approximate to 150 ps) in the base compared to devices from the other epi-layer (tau(B) approximate to 60 ps), which showed low reliability characteristics. Using XTEM images, it was found that devices with higher degree of reliability show abrupt base-emitter junction vs low-reliability devices, which appeared to have compositionally graded base-emitter hetero-interface.