The conductivity type of cuprous oxide (Cu2O) thin films is tuned by controlling the deposition potential of an electrochemical process in an acid cupric acetate solution containing sodium dodecyl sulfate. The morphology and chemical composition of the deposited Cu2O films are studied by SEM, XRD and XPS. The change of the conductivity type of Cu2O films is further studied through zero-bias photocurrent and Mott-Schottky measurements. The results indicate that the Cu2O films behave as n-type semiconductors when the overpotentials are low (potentials higher than -0.05 V) and p-type semiconductors when the overpotentials are high (potentials lower than -0.10 V). The transformation of conductivity from n-type to p-type comes from the competition reactions between forming Cu2O and forming metallic Cu from Cu2+. When the potential is lower than 0.10 V, most of Cu2+ are consumed by the growth of metallic Cu at the film/solution interface, so that the Cue} provided to grow Cu2O film are insufficient and copper vacancies form in the film, leading to the p-type conductivity. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.