Ultralow‐power, high‐resolution, pulsed‐laser photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies were carried out in molecular‐beam‐epitaxial GaAs/AlxGa1−xAs multi‐quantum‐well structures at 5 K. Fine structures were observed for the first time in the PLE spectra, both in the heavy‐hole and light‐hole excitonic regions. Most of the fine structures are considered to arise from monolayer fluctuations in the thicknesses of the GaAs wells. Dramatic changes in the line shapes and the peak positions of the PL and PLE spectra were observed by applying selective PL detection and excitation spectroscopic techniques.