Well size fluctuations have been observed in high quality GaAs-Ga0.75Al0.25As multi-quantum well structures having very sharp photoluminescence transitions. The effect of well size fluctuations appears as multiple peaks in both the heavy hole free exciton and the heavy hole donor bound exciton transitions. The observed energy separation of the peaks corresponds to what would be expected for a change in well thickness of 1/2 monolayer. The observed linewidths and the well size fluctuations suggest that these are interlayer rather than intralayer fluctuations. These results are different from earlier reported work. The very narrow emission lines reflect the excellent structural quality of the layers. A model to explain the effective half-monolayer well size fluctuations is proposed.