We report on the initial stages of GaAs and AlAs growth on Si substrates, focusing on that done using atomic‐layer epitaxy (ALE). ALE was performed on 3° off (100) substrates at 500 °C using an arsine and metalorganic gas source. Thin layers (5–350 monolayers) were examined using Auger electron spectroscopy, Raman scattering, transmission electron microscopy (TEM), and several other techniques. Measurements showed that ALE on Si substrates starts from three‐dimensional growth but changes to layer by layer growth at an early stage. Coverage is remarkably improved by initiating the growth from AlAs instead of GaAs. TEM images for AlAs indicate a relatively smooth surface and regular lattice arrangement on Si substrates. The coverage improvement is attributed to the selective‐adsorption and self‐limiting effects of ALE and proper arrangement of Al atoms on Si.