We have studied the temperature sensitivity of strained‐layer InGaAs/Ga(In)As(P)/GaInP separate‐confinement‐heterostructure quantum well lasers emitting at &lgr;∼980 nm. We observed that the lasers with GaAs confinement layers exhibited higher temperature sensitivity than those with GaInAsP confinement layers. It was also found that using the GaAs confinement layers, the lasing characteristics dramatically degraded at elevated temperatures, in particular, as the quantum well width was reduced. These phenomena could be attributed to a poor carrier confinement present in the case of InGaAs/GaAs quantum wells.