Sulfur incorporation in diamond was achieved by co-doping using H2S and trimethylboron. Particle induced X-ray emission, X-ray photoelectron spectroscopy, and secondary-ion mass spectroscopy confirmed the presence of sulfur, which was more concentrated in the near-surface region. The films were examined by Mott-Schottky analysis, open-circuit potentials in the presence of UV irradiation, and the thermoelectric effect. Diamond films grown with sulfur and limited amounts of boron were n-type; films grown at higher B/S ratios were p-type. The source of the donors is not known; they could arise from near-surface effects, defects, or impurity bands. (C) 2002 The Electrochemical Society.