Cathodoluminescence and electron beam induced current are used to investigate the degradation of the graded‐index separate‐confining heterostructure laser devices grown on silicon substrates. By examining the evolution of the microscopic electronic properties of these devices during operation or under electron beam bombardment, a better understanding of the initial mechanism of degradation in a laser device results: it is concluded from this study that the degradation starts in the vicinity of thep‐njunction before attaining the active layer or the formation of dark line defects. This starting of degradation is attributed to the point‐defect migration or coupling in the space‐charge region. The built‐in electrical field plus the nonradiative recombination of excesses carriers seems to be related to these phenomena. It is also pointed out that the technological processes for device fabrication have a strong influence on the degradation mechanism.