The surface structure of the reconstructed 6H-SiC(0001) Si-faces were investigated by using high resolution electron energy loss spectroscopy (HREELS). The 6H-SiC(0001) Si-faces exhibited the stable (root3 x root3)R30 degrees reconstruction when it was annealed in a Si flux at temperatures greater than 900 degreesC. The HREELS results verified that the adatom of the most stable root3 x root3 6H-SiC(0001) surface is the Si atom with only one dangling bond. Therefore, the root3 x root3 reconstruction stabilizes the 6H-SiC(0001)Si surface by compensating the dangling bonds of top-surface Si atoms with additional 1/3 monolayer Si atoms.