Layer intermixing in MeV Si‐implanted GaAs/AlGaAs superlattices (SLs) with doses between 3×1015 and 1×1016 /cm2 has been examined by transmission electron microscopy and secondary‐ion mass spectrometry. After either rapid thermal annealing at 1050 °C for 10 s or furnace annealing at 850 °C for 3 h, all the SLs showed a highly crystalline, defect‐free zone in the near‐surface region followed by a band of secondary defects, with the maximum density located about 1 μm below the surface. A totally mixed region, within the secondary defect band, occurred only in the SL implanted to 1×1016 Si/cm2 and annealed at 850 °C for 3 h. At lower doses or under rapid thermal annealing, only slight Al/Ga interdiffusion was observed, primarily in the layers that contained the high density of dislocation defects. For either annealing condition, the Si concentration profiles showed only slight broadening and they correlated with the distribution of secondary defects as well as with the depth of the intermixed layer. The effects of dynamic annealing and surface on the implantation energy dependence, i.e., MeV vs keV, of layer intermixing are discussed.