We have observed and analyzed a very rapid form of degradation caused by the optical excitation of GaAs/GaAlAs DH laser material. It consists of the very rapid (50 &mgr;/sec) development of ⟨110⟩‐oriented lines originating at a mechanically damaged area and restricted to the optically excited area. TEM analysis shows that the degraded region consists of an orthogonal array of misfit dislocations of 60° type at the interface between thep‐ternary layer and the active region. It seems likely that the dislocations are generated byglideas a result of the lattice misfit stress between GaAs and GaAlAs and that their energy of motion is supplied through nonradiative recombination events.