It has been found that selective thermal desorption of extremely thin oxide films on Si(lll) and Si(001) substrates is induced by electron beam irradiation. By using focused electron beams and this selective thermal desorption, a new nanofabrication technique has been demonstrated on oxide films. Open windows about 10 nm or less in width have been fabricated in oxide films by this technique. By pattern transfer from the open windows to Si and Ge films using surface chemical reaction, Si and Ge nanowires 10-20 nm in width have been fabricated.