By using of the nonlinear luminescence correlation technique, a new time resolved optical spectroscopy technique has been developed and applied to investigating of hot carrier relaxation processes in GaAs-GaAlAs multiple quantum well structures. It has been found that the well width has a significant effect on the relaxation processes. For a sample with Lz=40?, the time constant of the LO-phonon relaxation was found to be as long as 40ps. The physical me-chanism of this weakened electron-phonon interaction is also discussed.