We describe preparation of transparent nanocrystalline semiconductor sandwich electrodes. Specifically, TiO 2 -CdS and Cds-TiO 2 sandwich electrodes have been prepared by electrodeposition of CdS on TiO 2 and TiO 2 on CdS, respectively. Also described are the application of optoelectrochemical techniques for determination of the energy of the conduction band edge at thesemiconductor - liquid electrolyte solution interface (V c b ). Specifically, V c b has been determined for each semiconductor in nanocrystalline TiO 2 , CdS, TiO 2 -CdS and CdS-TiO 2 electrodes. For TiO 2 and CdS electrodes, V c b is -0.37 V (SCE) and -0.7 V, respectively, in aqueous solution at pH 2.0. Under similar conditions V c b for TiO 2 and CdS is -0.47 V and -0.4 V, respectively, in the corresponding TiO 2 -CdS sandwich electrode. Using the results of these and similar experiments, it has been possible to prepare energy level diagrams for nanocrystalline semiconductor sandwich electrodes. Implications for potential applications of these electrodes, particularly in regenerative photoelectrochemical cells, are considered.