The epitaxial growth of Si on a Si substrate using the molecular beam method in ultrahigh vacuum has been studied. We have used RHEED in the deposition system and differential interference microscopy for investigation of the surface structure and morphology of the films. It has been found that clean and smooth surfaces are obtained by preheating the Si substrate with a thin SiO 2 film at a high temperature (1240°C) for a short period (2 min). A Si(100) (2 × 2) surface structure was obtained on the clean surface after preheating. A Si(100) c(4 × 4) surface structure appeared on the epitaxial films for growth temperatures in the range between 700 and 800°C. All of the epitaxial films (450-1100°C) were free of stacking faults.