The growth control of pentacene thin films on SiO2/Si substrates is investigated by focusing on the relationship between the grain structure and flatness of the film surface. Pentacene thin films showing various grain structures are reproducibly controlled by changing the evaporation flux rate and substrate temperature. Atomic force microscopy analysis of the film surface indicates that the surface roughness is strongly related to the growth condition. In addition, flat-topped grains grown layer by layer are obtained among controlled grain structures, and a maximum grain size of 25 mum 2 is obtained. The surface roughness significantly decreases for the flat-topped grain. (C) 2004 Elsevier B.V All rights reserved.