Various factors influencing the temperature dependence of the threshold current of GaInAsP/InP lasers in the wavelength region of

m were measured in terms of the gain, the loss, the spontaneous emission, and the carrier lifetime. The effects of the intervalence band absorption influence the differential quantum efficiency or the loss, while the nonradiative recombination and the carrier leakage over the heterobarrier influence the carrier lifetime. It is shown from the measured results that both the absorption and the nonradiative components significantly influence the temperature characteristics of threshold current. The rapid increase in the threshold current near room temperature is a reflection of the increase in the intervalence band absorption. The heating effect due to the injection current is also significant. The possible maximum temperature of CW operation is expected to be as high as 150°C with optimized structural parameters.