Low temperature photoluminescence spectra measured from MBE GaAs/AℓxGa1-xAs superlattices with different excitation photon energies were analyzed to reveal superxlattice well thickness variations along the MBE growth direction. Due to their unique electrical and optical properties, semiconducting multi-quantum-well (MQW) structures are receivIng much attention fo; their applications in microstructure devices such as HEMT, SEED , and tunable lasers. The properties of MQW structures are greatly affected by the MQW heterointerface qualities, impurity contents, and layer thickness irregularities. So far, molecular-beam-epitaxy (MBE) prepared MQW structures are found to exhibit superior sample qualities i Tany respects, and a great deal of effort is being made to further advance MBE technology. The characterization of multi-layered structures, however, has not progressed as fast as the development of thin film growth methods. Among the various sample characterization methods, optical techniques offer certain advantages since the test results can be obtained in a relatively quick and simple manner. Besides, the nondestructive (or non-contact) nature of optical methods provides opportunities for repetitive evaluations, which improves accuracy in sample characterizations.