CdTe/CdS heterojunction solar cells show particular promise for large-scale terrestrial use. To evaluate these cells, thick films of CdTe and CdS have been grown and their structure and electrical properties determined. These films have been deposited on both single-crystal and fused-quartz substrates and on each other by close-spaced vapor deposition in H2 and by two-source vacuum evaporation. The influence of growth parameters on epitaxy and crystallite size was determined by scanning electron microscopy, and the electrical transport properties were investigated by conductivity and thermoelectric power measurements. The electrical mobility of the CdTe films on fused quartz shows an exponential dependence on E/kT, indicating that grain boundaries dominate the bulk mobility in the film. To achieve large crystallite sizes and high conductivity in reasonable deposition times, temperature/time profiles have been used to control nucleation and growth of the CdTe films. Post-deposition heat treatments in H2 have been used to increase the conductivity of the CdS films.