Formation of nanoparticle SiC (np-SiC) from three-layer Si/C/Si multilayers on Si(100) substrates were investigated using ultra-high-vacuum ion beam sputtering and post annealing by conventional furnace annealing (FA) and rapid thermal annealing (RTA). Fixing the thickness of bottom Si-layer at 50 nm, different thicknessses of the top Si and C layers were designed to study the effect of annealing on the reaction of np-SiC formation, that is, three-layer Si/C/Si structures with thicknesses of 50/200/50 nm by FA and 10/100/50 nm by RTA. There are almost no particle appears at 700 °C 1.0 h by FA due to low thermal energy. It was observed that np-SiC appeared at a density order about 108 cm-2 by FA at 900 °C for 1.0 h, but many np-SiC can be realized at 750 °C for annealing time as short as 1 min at a density order about 1010 cm-2 by RTA. The density is much higher than conventional nanoparticles synthesis using CVD or PVD. The reaction temperature of SiC is also lower than the conventional CVD or FA because of RTA enhanced SiC crystallization behavior at high heating rate. The annealing method influences the particle formation. The particle size, distribution and density are concerned with the top and middle layer thickness. Thermal energy is the diving force for the crystalline SiC formation through interdiffusion between C and Si.