This paper presents a study of spatial hole burning in the carrier concentration distribution of stripe geometry InGaAsP/InP double heterojunction lasers emitting at 1.3 &mgr;m. To study the behavior in detail we took the mutual relationships between the current flow in the resistive layer, the junction voltages between the active and confining layers, and the carrier concentration distribution in the active layer into consideration. Moreover, we treated the InP/InGaAsP/InP double heterojunction through an analysis of the heterojunction energy band structure. The analysis demonstrated that in narrow‐stripe lasers (?7‐&mgr;m stripe width) spatial hole burning in the carrier concentration distribution is greatly suppressed even at twice the threshold. We found the existence of a self‐focusing current flowing into the center of the stripe that acted to suppress spatial hole burning. The results suggest that in the quaternary lasers—the property of the active layer crystal, for example—long intraband relaxation time contributes greatly to the longitudinal‐mode behavior.