We report on the study of the submillimeter absorptivity of high‐Tcsuperconductors by a new method, the photothermal interference spectroscopy. Absorption in a sample leads to a temperature change of the sample and, by heat transfer, also of a gas volume adjacent to the sample and to a change of refractive index in the gas volume that we detect by an interferometric method. We demonstrate the feasibility of the method by determination of the absorptivity of high‐Tcsuperconducting YBa2Cu3O7−&dgr;samples for submillimeter radiation at a frequency near 1 THz. The absorptivity shows a peak atTc, that is most likely due to fluctuation effects, a strong drop belowTcand a finite value at low temperatures, with a peak near 15 K.