Secondary Ion Mass Spectrometry (SIMS) has been employed to study the diffusive behavior of combinations of Al and Cr thin films on polycrystalline CdSe. Samples were studied before and after annealing in a flowing N2 ambient at 350°C. Our results indicate that both Al and Cr will diffuse into CdSe under these conditions. However, Cr diffuses much more rapidly than Al. Also, Cr diffusion results in the uptake of oxygen by the CdSe and in a characteristic saddle-shaped profile for both Cr and oxygen. The results of this study further indicate that Al films as thin as 50 Å sandwiched between the CdSe and Cr films can act as an effective barrier to the diffusion of Cr.