Cyclic voltammograms have been obtained under a variety of conditions using a semiconducting photoelectrode or a circuit containing a diode in series with a metallic electrode. Simulations of the voltammetry of both types of systems were performed using a model circuit in which electrode nonideality, double-layer capacitance, and parallel resistance effects were accounted for quantitatively. The simulated voltammograms were in excellent agreement with the experimental data for a diode/electrode circuit, yielding a reliable description of the shapes of the voltammograms as well as of the voltage dropped across the diode element as a function of the total potential dropped across the circuit. The digital simulations were in good agreement with the voltammetry of p-Si/CH3OH-CoCp2+/0 contacts at high light intensities, but could not quantitatively describe the shapes of the voltammograms at low light intensities.