A nanoscale fabrication process compatible with present Si technology is reported. Preimplanted contact arrays provide external leads for scanning tunneling microscope (STM)-defined dopant patterns. The STM's low energy electron beam removes hydrogen from H terminated Si(100) surfaces for selective adsorption of PH3 precursor molecules, followed by room temperature Si overgrowth and 500 degreesC rapid thermal anneal to create activated P-donor patterns in contact with As+-implanted lines. Electrical and magnetoresistance measurements are reported here on 50 and 95 nm-wide P-donor lines, along with Ga-acceptor wires created by focused ion beams, as a means for extending Si device fabrication toward atomic dimensions. (C) 2004 American Vacuum Society.