We report the spontaneous formation of well-aligned indium (In) hillock on silicon substrate with a thin Au film as buffer layer by using DC magnetron sputtering method. The morphologies and the microstructures have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The mechanism of the hillock formation can be described as follows: (1) low-dimensional (LD) alloy surface formation; (2) In adatom diffusing on LD-alloy surface to form cluster; (3) clusters coalescence to form two-dimensional island (2D-island)- and (4) 2D-islands grow up and form hillock. (c) 2006 Elsevier B.V. All rights reserved.