Single and polycrystalline samples of Cd3P2 have been prepared. Undoped samples are n-type with carrier concentrations between 1017 and 1018 cm-3. The thermoelectric power of these samples goes up to -170 μV/°C at 300°K. Mobility values up to 3000 cm2/V sec at 300°K were measured. The mobility of single crystals varies in the extrinsic range near room temperature proportionally to T-1.1 (T is temperature). Optical measurements indicate an optical band gap of approximately 0.5 eV. The results of annealing experiments support the assumption that the high electron concentration of undoped samples is due to phosphorus vacancies. The doping properties of various elements have been studied. Copper introduces what is probably a deep-lying acceptor level, but p-type samples could not be obtained.