We use frequency-dependent capacitance spectroscopy to study electron tunneling and storing in nanocrystalline silicon (nc-Si) floating-gate double-barrier structure (SiO2/nc-Si/SiO2) fabricated in situ by plasma oxidation and layer-by-layer deposition in a plasma-enhanced chemical vapor deposition system. Distinct size- and firequency-dependent capacitance peaks due to Coulomb blockade charging and quantum-confinement effects have been observed by capacitance spectroscopy in a large ensemble of nc-Si dots at room temperature for the first time in a SiO2/nc-Si/SiO2 system. This finding demonstrates that the Coulomb blockade for electrons in nc-Si dots is larger than the size fluctuation effects on the quantum confinement for our nc-Si floating-gate double-barrier structure. (C) 2004 American Vacuum Society.