We demonstrate that by controlling surface state properties with a simple and rapid aqueous fluoride ion treatment, excellent electronic operation can be achieved on intrinsic Si nanowires without bulk doping, thereby taking advantage of the increase in surface-to-volume ratios in these diminutive structures. Forming the fluoride-decorated (F-decorated) oxide surface significantly increases the conductivity by more than one order of magnitude over the oxide surface and more than three orders of magnitude over the oxide-free H-terminated surface. This provides a methodology that might, in some instances, sidestep the difficult-to-control impurity doping of nanodevices.