The dependence of the characteristic temperatureT0on the cavity length and lasing wavelength is theoretical and experimentally analyzed. The devices are straight separate confinement heterostructure lasers with active layer thickness of 30 and 12 nm grown by low temperature liquid phase epitaxy. The recent observation that for very short lasersT0is an increasing function of the cavity length is confirmed, and explained in terms of the threshold current cavity length dependence. The temperature dependence of the threshold currentIthgivesT0as high as 307 K for a quantum well laser with cavity lengthL=168 &mgr;m. ©1995 American Institute of Physics.