(AlAs)1/2(GaAs)1/2fractional‐layer superlattices (FLSs) are grown on a (001) GaAs substrate, tilted slightly in the [1¯10] direction using metalorganic chemical vapor deposition. The periodic structures are analyzed by x‐ray superlattice satellite diffraction. The results suggest that the step flow mode from monolayer step is a dominant crystal growth process. However, the satellite intensities drastically decrease under heavy Si impurity doping conditions (n>2×1017cm−3), showing that impurity‐induced disordering occurs during fractional‐layer growth. The growth mechanism under impurity doping conditions is also discussed.