Conductive-atomic force microscopy is used to electrically characterize a nanometric metal-SiO2–Si (n+) system with Au nanocluster inclusions in SiO2. The system shows a marked rectifying behavior at room temperature with a threshold voltage function of the cluster size. This behavior is interpreted crossing physical considerations on metal-oxide-semiconductor structure and on double barrier tunnel junction device. The system fabricated and analyzed is proposed as a possible basic component for nanoelectronic circuits working at room temperature.