We have observed mid-infrared photoluminescence at &lgr;≈10 &mgr;m between conduction subbands in GaAs quantum wells. As for regular band-to-band interband photoluminescence spectroscopy, carriers are optically generated in the quantum wells using an interband optical pumping. At room temperature, the excited subbands of the quantum wells are thermally populated. Most of the carriers recombine nonradiatively through electron–phonon interactions, but a fraction of the carriers in the excited subbands recombine radiatively and give rise to the intersubband spontaneous emission in the 10 &mgr;m wavelength region. The intersubband photoluminescence is polarized along the growth axis of the quantum wells as expected from intersubband polarization selection rules. The emitted optical power is in the nW range and the quantum efficiency is found in agreement with calculations taking into account the radiative subband lifetimes. The emission is analyzed in terms of a blackbody emission of an electron gas in a two-dimensional confined system. ©1997 American Institute of Physics.