The spectral width of (GaAl)As cw single‐mode diode lasers varied linearly with reciprocal output power at 300 K with a slope 50 times greater than that predicted by the Schawlow‐Townes expression without partial inversion. While the spectral narrowing observed at 77 K for constant mode power is consistent with the predicted temperature dependence of the partial inversion contribution, the magnitude of the broadening can not completely be attributed to partial inversion.