Researchers from the Department of Electronic Ceramics K5 at the Jožef Stefan Institute, Tadej Rojac and Barbara Malič, together with collaborators from Germany and Austria, have published an article in Reports on Progress in Physics titled “How semiconducting are ferroelectrics: the fundamental, optical and transport gaps of Na₀.₅Bi₀.₅TiO₃–BaTiO₃ and NaNbO₃”.The study addresses the pressing issue of determining and interpreting the so-called band gap in ferroelectrics. Using two ferroelectric perovskites as examples, the paper discusses the differences between the fundamental, optical, and transport bandgaps, their determination using methods such as optical spectroscopy and X-ray photoelectron spectroscopy, as well as the interpretation of the band gap in the context of the chemistry and physics of point defects. The results provide entirely new insights into the engineering of electronic and optoelectronic properties of ferroelectric materials.