Abstract: The invention relates to a process for producing photonic crystals by first providing an inorganic photoresist which, on illumination with energy greater than the electronic band gap of the photoresist, exhibits a phase alteration. Illumination of the photoresist with a laser beam whose energy is lower than the electronic band gap of the photoresist but whose intensity at the focal point is so high that nonlinear effects occur there nevertheless results in a phase alteration in the photoresist. Thereafter, the illuminated photoresist is exposed to an etching solution which preferentially dissolves one phase of the photoresist, and the developed photoresist is finally removed therefrom as a photonic crystal. Inorganic photonic crystals produced by the process according to the invention are suitable for completely optical systems, circuits and components for optical telecommunication or computer systems.