The covalent attachment of a pyrrolyl monolayer has been efficiently achieved by directly exposing pyrrole molecules to the clean Si(100)-(2 x 1) surface. The high-resolution electron energy loss spectroscopy (HREELS), and X-ray photoelectron spectroscopy (XPS) studies show that the robust pyrrolyl monolayer is directly bonded to the Si(100) surface via the Si-N linkage with the preservation of the pyrrolyl ring structure. The as-prepared pyrrole-modified silicon surfaces can serve as templates for further electrochemical polymerization of polypyrrole thin films onto silicon substrates, providing new opportunity for fabrication of new polypyrrole/silicon heterojunctions with improved performance.