InGaAsP epitaxial layers were excited by a Nd: YAG laser (λ=1.064 µm), directly, or through InP cladding layers. The photoluminescence intensity pattern of the InGaAsP active layer in InP–InGaAsP double heterostructure (DH) wafers remained unchanged even of excitations exceeding 100 kW/cm2, when excited through InP cladding layers. This result should be compared with an A1GaAs–GaAs system, where photoluminescence degradation is observed for about 5 kW/cm2 excitation. However, photoluminescent dark regions were formed when the InGaAsP surface was excited directly. Moreover, once these dark regions were formed, they grew continuously without further excitation. The observed dark regions are not due to InGaAsP bulk degradation, because the degraded photoluminescence intensity could be recovered to the initial intensity by rinsing the InGaAsP surface with dilute HC1, which does not attack a bulk InGaAsP crystal.