We have investigated sulfur incorporation and the effects of H2S addition on the crystal quality and electrical properties of sulfur-doped homoepitaxial (100) and (111) diamond grown by microwave plasma-assisted chemical vapor deposition. In the case of (100) homoepitaxial growth, adding a small amount of H2S effectively improved the crystal quality, whereas adding an excess of H2S degraded the crystal quality. The amount of incorporated sulfur increased with increasing amounts of H2S. At the same time, the amount of undesirable silicon impurities decreased. Adding H2S in the range of 50-100 ppm yielded a high-quality S-doped diamond. In a temperature range of 250-550 K, the high-quality S-doped homoepitaxial (100) diamond showed n-type conduction by Hall-effect measurements. The electrical properties of S-doped (100) diamond were sensitive to the quality of the crystal. The crystal quality of the S-doped(lll) homoepitaxial diamond was poorer than that of the (100) diamond. The quality of the S-doped(111) diamond was insensitive to the amount of additional H2S. The resistivity of the (111) diamond was very high compared to that of the (100) diamond. The resistivity of the undoped (111) diamond was lower than that of the S-doped (111) diamond. The Hall effect measurement could not be performed on the (111) homoepitaxial diamonds.