We report here on the formation of robust and entirely hollow sing le-crystal line silicon nanotubes, from various tubular to conical structures, with uniform and well-controlled inner diameter, ranging from as small as 1.5 up to 500 nm, and controllable wall thickness. Second, and most important, these nanotubes can be doped in situ With different concentrations of boron and phosphine to give p/n-type semiconductor nanotubes. SixGe1-x-alloy nanotubes can also be prepared. This synthetic approach enables independent and precise control of diameter, wall thickness, shape, taper angle, crystallinity, and chemical/electrical characteristics of the nanotubular structures obtained. Notably, diameter and wall thickness of nearly any size can be obtained. This unique advantage allows the achievement of novel and perfectly controlled high-quality electronic materials and the tailoring of the tube properties to better fit many biological, chemical, and electrical applications. Electrical devices based on this new family of electrically active nanotubular building-block structures are also described with a view toward the future realization of nanofluidic FET devices.