Monitoring of the layer-by-layer growth of an AlAs/GaAs superlattice is performed using coaxial impact-collision ion-scattering spectroscopy. By exploiting high-frequency time-of-flight analysis, real-time observations of the intensity variation from Ga signals, which indicates the surface coverage of GaAs, are achieved. The intensity increases when GaAs is grown on AlAs, and the rise time of the intensity variation agrees well with the time for one-monolayer growth of GaAs.