Qualified GaAlAs/GaAs oxide isolated stripe geometry DH lasers, degraded at temperatures up to 90 °C, have been examined using the cathodoluminescence (CL) and electron beam induced current (EBIC) modes of the scanning electron microscope, and by transmission electron microscopy in a 1‐MeV TEM. The main features observed in the EBIC and CL images in the plane of the heterojunction of the degraded lasers were bright and dark bands running parallel to the stripe, together with brightened mottled regions extending well outside. The separation of the bands and the extent of the mottled region is dependent on the width of the stripe. This general pattern is modified considerably near to the facets of the lasers. Calculations of strain profiles for the different laser types suggested that these phenomena can be explained in terms of a model of operation induced, strain enhanced, defect migration. Small dislocation loops seen at the edges of the stripe, using transmission electron microscopy appear to support this model.