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We present a detailed study of the electronic properties of individual silicon nanocrystals (nc-Si) elaborated by low-pressure chemical vapor deposition on 1.2 nm thick SiO2 grown on Si (100). The combination of ultrathin oxide layers and highly doped substrates allows the imaging of the hemispherical dots by scanning tunneling microscopy. Spectroscopic studies of single dots are made by recording the I(V) curves on the Si nanocrystal accurately selected by a metallic tip. These I(V) curves exhibit Coulomb blockade and resonant tunneling effects. Coulomb pseudogaps between 0.15 and 0.2 V are measured for different dots. Capacitances between 0.2 and 1 aF and tunnel resistances around 5×109 Ω are deduced from the width and height of the staircases. The charging and confinement energies deduced from the I(V) curves are in good agreement with a modified orthodox model which includes the quantification of electronic levels.