The effect of substrate temperature (Ts) on the initial nucleation of hydrogenated amorphous silicon (a‐Si:H) prepared by glow discharge has been studied using aninsituellipsometry probe. Evidence in the ellipsometry data for clustering of Si–Si bonds at nucleation centers, for films prepared withTs∼250 °C, gradually disappears asTsis reduced below ∼200 °C. This indicates that the clustering process accompanies defect reduction during growth commonly observed in glow dischargea‐Si:H asTsis increased. ForTs>200 °C, a sufficiently high surface mobility may enable the depositing species to bind at lower energy sites, thus explaining the observed results.