We have employed photoluminescence spectroscopy to determine the interdiffusion of Al and Ga in (Al,Ga)As/GaAs quantum wells. The luminescence due to the n=l electron to heavy hole transition in these wells before and after anneal was measured. A variational calculation was employed to determine the expected position of this luminescence peak both before and after the anneal. A single diffusion coefficient, D, was used to model the interdiffusion of the Al and Ga and from the shifted position of the luminescence peaks under various anneal conditions of time and temperature its value was determined. These measurements were performed as a function of temperature to yield ΔE where D = D
0e -ΔE/KT. This diffusion coefficient was also studied as a function of the initial Al composition in the cladding layers which ranged from 0.3 to 1.0.