Some degradation modes of 1.3 and 1.55 &mgr;m buried heterostructure distributed feedback (DFB) lasers grown by liquid‐phase epitaxy are clarified. A degradation mode induced by the inhomogeneous optical‐field distribution along the laser cavity is found to exist in DFB lasers. In most DFB lasers, the interface degradation between first growth‐step (double heterostructure) layers and second growth‐step (burying) layers occurs in the same manner as Fabry–Perot lasers.