We measured electrical conductances in single crystalline boron nanobelts having a-tetragonal crystalline structure. The doping experiment of Mg was carried out by vapor diffusion method, We obtained ohmic contacts to both pure and Mg-doped nanobelt by metal electrodes of Ni/Au bilayer. From the temperature dependence of electrical conductance, we found that the pure boron nanobelt is a semiconductor. The electrical conductivity of pure boron nanobelt was estimated to be on the order of 10(-3) (Omega cm)(-1) at room temperature. After Mg vapor diffusion. the electrical conductance increased by a factor of 100 but a transition to metal was not observed. (c) 2005 American Vacuum Society.