We report, for the first time, the identification of extrinsic dislocation loops lying on the {100} planes with 1/2⟨100⟩ types of Burgers vectors in a zinc blende structure in InGaAsP lattice matched to InP. These dislocation loops generated only in nonradiative recombination assisted point‐defect motion process under intensed laser light, and form the ⟨100⟩ type dark line defects in degraded 1.3 &mgr;m wavelength laser diodes.