The catastrophic degradation of GaAlAs DH laser diodes is examined with the application of pulsed or dc current. The dependence of the pulsewidth on the degradation is measured using samples with or without facet coating. The light outputPDat which the catastrophic degradation occurs decreases with an increase in the pulsewidth in the pulsewidth range 100 nsec to 10–50 &mgr;sec, andPDis constant over the pulsewidth of 10–50 &mgr;sec. The sample with an Al2O3film coating has the highestPD. Photoluminescence patterns of the active layer in degraded samples both with and without facet coating show the growth of DLD’s in the ⟨110⟩ direction from the vicinity of a facet in the stripe region.