The nonamplified spontaneous emission of AlGaAs single quantum well graded index separate confinement heterostructure laser diodes has been measured for photon energies between 1.35 and 2.05 eV and at pump currents up to 19 kA cm-2 and optical flux densities up to 35 MW cm-2. The spectra are very complex and we observe the following three features. First, the spontaneous emission intensity increases slowly with current, even above threshold. Second, the carrier temperature increases slightly above the lattice temperature, 28 K at a pump rate of 1.5×1029 cm-3 s-1. Third, at high power densities the high-energy spontaneous emission at a photon energy of 1.9 eV increases dramatically.