A nanowire includes a single crystalline semiconductor material having an exterior surface and an interior region and at least one dopant atom. At least a portion of the nanowire thermally switches between two conductance states; a high conductance state, where a high fraction of the dopant atoms is in the interior region, and a low conductance state, where a lower fraction of the dopant atoms is at the interior region and a higher fraction of the atoms is at the exterior surface. A method to select the conductance of the nanowire increases a temperature of the nanowire at least in a local region to a programming temperature to thermally activate diffusion of a dopant atom into a bulk region of the single crystalline semiconductor material and decreases the temperature of the nanowire at least in the local region to a second temperature to immobilize dopant atoms in the bulk region, the second temperature being below the programming temperature, wherein immobilized dopant atoms in the bulk region produce a desired high or low conductance state in the nanowire. The method can be used to initially configure and to reconfigure a circuit incorporating the nanowire.