We have confirmed biexciton formation in an organic-inorganic hybrid quantum-well material (C 4 H 9 NH 3 ) 2 PbBr 4 by photoluminescence and two-photon absorption measurements. The biexciton has extremely large binding energy, 60meV, which to our knowledge is the largest value ever reported for a semiconductor. By analyzing the spectrum of biexciton luminescence, the biexciton gas temperature was found to be much higher than the bath temperature due to a higher local temperature arising from the large biexciton binding energy.