We report the fabrication and electrical characteristics of an ultrathin nanocrystalline-silicon/amorphous silicon oxide double barrier resonant tunneling diode. The cross-section high resolution TEM photographs indicate the layered structure and the crystallinity of nanocrystalline Si with an average grain size of 10 nm. In this prototype device, a series of reproducible conductance peaks have been observed as a function of the applied gate bias at room temperature. The real voltage spacing of 0.38V between the peaks is determined from an equivalent circuit. The results are in agreement with the theory of Coulomb blockade effect using 1.1 aF of capacitance in single Si nanocrystallite. We conclude that the observed behavior results from resonant tunneling, which is strongly influenced by Coulomb blockade effect, through the zero-dimensional states in the well isolated silicon quantum dots.