Low molecular weight poly(ethylene glycol) silanes (PEG silanes) have been grafted onto the surface of silicon wafers in a one-step procedure yielding ultrathin and stable PEG monolayers. Structural investigation by means of X-ray reflectivity provided data on the thickness of the PEG monolayers. The layer thickness varied between 10 and 17 A depending on the PEG silane concentration applied. These results have been confirmed by X-ray photoelectron spectroscopy measurements Atomic force microscopy data indicate very smooth and homogeneous coverages with roughnesses of less than 3 Angstrom . The PEG layers are hydrophilic as determined with advancing water contact angles between 36 and 39 degrees.