Amorphous SiN/amorphous Si/amorphous SiN sandwiched structures with two different thicknesses of amorphous Si are prepared by plasma-enhanced chemical vapor deposition. Raman spectra demonstrate the formation of Si quantum dots (QDs) when the laser energy is above 320 mJ and the sizes can be controlled as small as 2.8 nm and 4.7 nm, which suggests that the size-controllable Si QDs can be formed due to constrained confined effect in sandwiched structures. Room temperature electroluminescence (EL) can be detected when the applied voltage is above 10 V, and the intensity varies under different laser energies. The EL spectrum peaks are at 680 nm (2.8 nm QDs) and 720 nm (4.7 nm QDs) which are attributed to the radiative recombination of injected electrons and holes within the Si QDs.