The scanning tunneling microscope (STM) has been used to fabricate grooves a few nm wide at room temperature by extracting atoms one by one from the Si(111)7×7 surfaces. When the direction of modification is parallel to the basic vector of Si(111)7×7 surfaces, grooves formed by such a process have atomically straight edges and lateral features as small as one 7×7 unit cell wide. The critical current under various voltages for fabricating grooves is measured. The modification mechanism is discussed based on the experiment data in this letter. ©1995 American Institute of Physics.