Manganese–cobalt–zinc oxide films are deposited on graphite foils by a dry process, simpler one-step radio frequency sputtering with different substrate treatment temperatures and bias potential. The best long-term operational stability (only reduce about 7% specific capacitance at the 8000th cycle of potential cycling) and good specific capacitance are obtained at a substrate treatment temperature of 200°C and without substrate bias potential. Furthermore, the lower the substrate treatment temperature, the better the stability. Moreover, the specific capacitance of the manganese–cobalt–zinc oxide electrode decreases with increasing substrate bias potential.