The surface morphology of MnSi thin films grown on Si(111)-7 x 7 substrates was investigated by systematically changing the amount of deposited Mn. A new 3 x 3 surface reconstruction was found at the very initial growth stages, whose atomic configuration was analyzed both experimentally and theoretically. At a coverage of 0.1 monolayers, the formation of nanometer-sized MnSi islands was observed in coexistence with Mn nanoclusters that fit within the 7 x 7 half unit cell. With increasing Mn deposition, the MnSi islands grow, develop extended flat tops and eventually coalesce into an atomically flat film with a high corrugated root 3x root 3 reconstruction punctuated by several holes. The successive film growth mode is characterized by the formation of MnSi quadlayers with a low corrugated root 3x root 3 reconstruction. (C) 2013 Elsevier B.V. All rights reserved.