Although many advances in the field of II–VI laser diodes have been reported since the first demonstrations of II–VI lasers in the summer of 1991, several obstacles still exist along the path towards long-lived II–VI laser diodes. This article will discuss mechanisms which lead to the degradation of the pseudomorphic separate confinement heterostructure laser diodes. Point defects and stacking faults are shown to play an important role in the degradation of these laser diode structures. The importance of controlling the substrate temperature to control the strain will be shown; a method to improve substrate temperature control will be provided.