An x‐ray study of annealing effects in Si0.65Ge0.35/Si strained‐layer superlattices grown by molecular‐beam epitaxy (MBE) at 500 °C is reported. The samples were subjected to thermal treatments between 600 and 698 °C, and the superlattice peaks and Si(004) peak were monitored at both low and high angles using powder and double crystal diffractometries. The interdiffusion coefficient of the average composition, obtained from the decay in intensity of the first superlattice peak about (000), was found to be similar to the results obtained from satellites about (004). This leads to the important conclusion that the diffusion coefficient can be obtained using the high‐angle technique, which is generally faster and less susceptible to experimental errors. The comparison between the two groups of measurements further emphasizes the fact that the critical slopes of the intensity plots should be excluded from the calculation of the diffusion coefficient.