We analyzed the Raman spectra and x‐ray diffraction of two GaAs/Al0.3Ga0.7As superlattices grown by molecular‐beam epitaxy on a 4 ° misoriented (001) GaAs substrate and an exactly (001)‐oriented GaAs substrate respectively. From the frequency shifts of the longitudinal‐optical‐ (LO) confined phonons in the Raman spectra and the variation in linewidths of both the LO‐confined phonons and the satellite peaks in x‐ray diffraction, we found that the 4 ° misorientation of the GaAs substrate from (001) toward [110] direction improves the interface quality of the superlattices.