A relatively simple stress modulation technique, based on optical absorption, for measuring the interband transitions in semiconductor electrodes in electrolytes is described. The modulated stress is applied to the semiconductor by modulating the strain of an attached piezoelectric transducer. Stress modulated photoelectrochemical spectra in the vicinities of the minimum interband gaps of ann‐TiO2single crystal electrode and a thin‐filmn‐CdSe electrodeinsituare presented.