The nanometer-scale interface morphology of top Si/buried oxide in SIMOX (separation by implantation of oxygen) and the influence of nano-size Si clusters to the electronic properties of the buried oxide (BOX) layer were studied by Conducting Atomic Force Microscopy (C-AFM). With C-AFM, the interface morphology and the current-voltage (I-V) curves of the BOX can be obtained simultaneously. The results found that the interface of Si/BOX in SIMOX had a very smooth surface morphology and there were some nanometer-size Si clusters distributed in the BOX, forming conducting channels. Furthermore, the high-resolution transmission electron microscope (HRTEM) and spreading resistance probe (SRP) were used to characterize the BOX. (C) 2003 Elsevier B.V. All rights reserved.