A consistent method to characterize the temperature dependence of bulk InGaAsP semiconductor laser diodes is presented. Independent measurements of the gain and spontaneous emission spectra are conducted, and the spectra are calibrated using their fundamental relationship. This procedure will provide a unique approach to extract precise values for laser diode parameters such as quasi-Fermi level separation, peak modal gain, and total loss. The radiative and nonradiative current densities can then be calculated as a function of temperature and injection current. By comparing the measured data with a theoretical model, the carrier density is calculated. Important phenomena contributing to the strong temperature dependence of long-wavelength bulk InGaAsP/InP lasers are highlighted. ©1997 American Institute of Physics.