We have observed precise geometrical correlation between ``dark‐line''‐type defects characteristic of the rapid degradation mode of (optically pumped) AlGaAs DH laser material with etch pit features in the vicinity of the GaAs/p‐AlxGa1−xAs heteroboundary. The patterns observed strongly suggest that the degradation is associated with creation or possibly decoration of dislocation linesinclined tothe {100} junction plane, and that the commonly observed ⟨100⟩ orientation of the dark lines is due to statistical aggregation of such inclined lines.