Sandwiched structures (a-SiNx/a-Si/a-SiNx) have been fabricated by the plasma enhanced chemical vapour deposi-tion technique. A Si nanocrystal (nc-Si) layer was formed by crystallization of an a-Si layer according to the constrainedcrystallization principle after quasi-static thermal annealing at 1100℃ for 30min. Transmission electron microscopy(TEM) and Raman scattering spectroscopy clearly demonstrated that nc-Si grains were formed in the as-deoositeda-Si layer after annealing. The density of nc-Si grains is about 1011cm-2 as shown by TEM photograplasx Usingcapacitance-voltage (C-V) measurements we investigated the electrical characteristics of the sandwiched structures.The charge storage phenomenon of the nc-Si layer was observed from the shift of flat-band voltage (VFB) in C-V curvesat a high frequency (1 MHz). We estimated the density of nc-Si grains to be about 1011cm-2 from the shift value ofVFB, which is in agreement with the result of TEM photographs. At the same time, we found that the shift of VFBincreased with the increase of the applied constant dc voltage or the thickness of the nc-Si layer.