Abstract: An ohmic contact includes a metal boride layer on a semiconducting diamond layer. The metal boride preferably includes boron and a transition metal and, more preferably, a refractory metal. Heating of the metal boride layer and diamond during fabrication forms a highly boron-doped surface portion of the semiconductor diamond by boron diffusion. Alternately, the highly doped surface portion may be formed by selective ion implantation, annealing to form a graphitized surface portion, and removing the graphitized surface portion by etching to thereby expose the highly doped surface portion. The highly doped surface portion lowers the electrical resistivity of the contact. In addition, an interface region of a carbide may also be readily formed by heating. The carbide interface region enhances mechanical adhesion of the metal boride and also serves to lower the electrical resistance of the contact.