Capacitance-voltage (C-P) and electrostatic force microscopy (EFM) measurements on Si nanocrystals (Si-NCs) formed by using the sonochemical method were carried out to investigate the charging effects of the Si-NCs. Transmission electron microscopy images and atomic force microscopy images showed that the Si-NCs were created inside the SiO2 layer. The C-V curve and the EFM image showed that the Si-NCs embedded in the SiO2 layer experienced charging effects. The macroscopic surface charge density determined from the C-V curve was in reasonable agreement with the microscopic local value obtained from the EFM image. The present results indicate that the EFM technique might provide a promising method for investigating charging effects in various kinds of nanocrystals embedded in the insulating layer. (C) 2007 Elsevier B.V. All rights reserved.