A model is developed for the polarization dependent refractive index of interdiffused AlGaAs/GaAs quantum well at room temperature for wavelengths ranging from 0.6 to 2 &mgr;m. The present model is based on a semianalytic and semiempirical method through the Kramers–Kro¨nig transformation. The multi-quantum-well structures, including the exciton effect and above barrier gap contributions, are fully considered in this model. The distinct structures at energies of theE0,E0+&Dgr;0,E1,andE2critical points are revealed. Moreover, the birefringence at room temperature is also analyzed in the wavelength range varying from 0.7 to 1.0 &mgr;m. The calculated refractive index results are in satisfactory agreement with the experimental measurements over the quantum well band edge, i.e., 0.8–0.9 &mgr;m. The effect of interdiffusion on the change of refractive index is discussed. The polarization dependent absorption coefficients are also calculated with all the bound excitons, and results agree well with experiments. These results are important, since refraction index in a particular wavelength region of interest, where experimental data are not available, can be determined and thus are very useful in the design of devices. ©1997 American Institute of Physics.