This chapter reviews distinct photonic/electronic properties originating from built‐in nanostructures in transparent oxide‐based materials, emphasizing potential of nanostructures hidden in crystal structure. Materials focused on are oxychalcogenides LaCuOCh (Ch = chalcogen ion) and homologous oxides InGa03 (Zn0) m (m = integer) having naturally formed multi‐quantum well structures and 12Ca0‐7Al203 (C12A7) with a unique nanoporous structure. Novel functions and devices arising from the built‐in nanostructure are: (1) modulation doping of positive holes and room‐temperature stable exciton in LaCuOCh, (2) high‐performance transparent field‐effect transistor fabricated in InGa03(Zn0)5 epitaxial thin films, and (3) conversion of insulator to persistent electronic conductor by carrier doping in 12Ca0‐7Al203 (C12A7). These examples demonstrate realization of excellent photonic and electronic features in oxide‐based materials applicable for emerging devices. Present attainments open a new frontier of material science, paving a way to “invisible oxide electronics.” UV‐LED (light source, transparent PN‐junction and transparent conductive line) are key components for invisible circuits.