Ti-catalyzed Si nanowires were grown by molecular-beam epitaxy using Si2H6 as the Si source gas and As and B from effusion cells as the doping sources. In situ doping of the Si nanowires was used to form rectifying p-n junctions. Recombination-generation current and series resistance can be observed in selected voltage regions. A structure containing n-type nanowires and a tungsten gate layer was fabricated with the nanowires remaining attached to the substrate at their original growth locations. The current-voltage characteristics of the in situ vertical gated structure can be modulated by an applied gate voltage. (c) 2005 The Electrochemical Society.