Thin film electrodes of have been prepared by vapor deposition of Ti on a quartz substrate followed by partial oxidation to leave a thin Ti layer as back‐side contact. The electrodes were characterized for their photoelectrochemical activities both on illumination through the electrolyte and through the substrate (back‐side illumination). The transparent substrate made it possible to record the action spectrum for back‐side illumination down to 250 nm. Simple theory has been used to estimate bandgap, flatband potential, and doping density. Observed bandshifts in the action spectra due to changes in doping density and electrode potential have been shown to be in accordance with theory.