Degradation modes of InGaAsP/InP buried heterostructure lasers are classified into three types; rapid, saturable, and gradual degradation. The influences of the temperature dependence of threshold current and the carrier leakage through the buried regions on degradation are described. Lasers that can operate cw above 90°C and show only gradual degradation can be expected to have a mean-time-to-failure of more than 107 h at 25°C.