The electrical properties of ZrO2-CeO2 solid solutions are investigated in detail as functions of the temperature between 200 and 1000 degrees C and of the ceria molar fraction between 16 and 100% (pure CeO2). The samples are studied by combining impedance spectroscopy, ionic transport number and thermoelectric power measurements so as to define the role and the contribution of hole and electron carriers to the conductivity mechanism. In particular, the transition from p- to n-type conductivity of undoped CeO2 at 750 degrees C is clearly demonstrated. The conductivity dependence on the oxygen partial pressure is also studied in the ZrO2-80 mol% CeO2 composition that exhibits the highest electronic conductivity.