The covalent attachment of N-methylallylamine (MAA) and N,N-dimethylallylamine (DMAA) on Si(111)-7×7 was investigated with high-resolution electron energy loss spectroscopy (HREELS) and X-rayphotoelectron spectroscopy (XPS). Experimental results showed that MAA chemisorbs dissociatively on Si(111)-7×7 through the cleavage of its N−H bond, while DMAA is covalently bonded to the silicon surfacevia a [2+2]-like cycloaddition between its CC group and the adjacent adatom−rest atom pair. This studydemonstrates that the selective organic functionalization of silicon surfaces can be achieved by fine-tuningmolecular structures.