The longitudinal mode behavior of AlGaAs lasers withn‐type cladding layers doped with Se and Si is reported. The longitudinal mode of the lasers with highly Se‐doped cladding layer is stabilized, and large hysteresis of mode jump is observed as temperature changes. In the case of highly Si‐doped cladding layers, however, the mode hops to the adjacent one and no hysteresis is observed. These phenomena are explained by the difference in thermal activation energy between Se‐ and Si‐relatedDXcenters.