We report on the fabrication and electrical characterization of epitaxial Schottky diodes of a half-metallic ferromagnet on an oxide semiconductor. La _0.67 Sr _0.33 MnO ₃ thin films are grown by pulsed laser deposition on niobium-doped SrTiO ₃ semiconductor substrates with two doping concentrations and a TiO ₂ surface termination. The current across the diodes is dominated by thermionic emission and shows high rectification and low reverse bias leakage. At room temperature, the Schottky barrier height is 0.95 eV (0.65 eV) and the ideality factor is 1.08 (1.18) for the diodes with a low (high) doped semiconductor. With decreasing temperature the Schottky barrier height decreases and the ideality factor increases. © 2004 American Institute of Physics.