Applying the concept of materials design for transparent conductive oxides to layered oxychalcogen ides, several p-type and n-type layered oxychalcogen ides were proposed as wide-gap semiconductors and their basic optical and electrical properties were examined. The layered oxychalcogen ides are composed of ionic oxide layers and covalent chalcogenide layers, which bring wide-gap and conductive properties to these materials, respectively. The electronic structures of the materials were examined by normal/inverse photoeinission spectroscopy and energy band calculations. The results of the examinations suggested that these materials possess unique features more than simple wide-gap semiconductors. Namely, the layered oxychalcogen ides are considered to be extremely thin quantum wells composed of the oxide and chalcogenide layers or 2D chalcogenide crystals/molecules embedded in an oxide matrix. Observation of step-like absorption edges, large band gap energy and large exciton binding energy demonstrated these features originating from 2D density of states and quantum size effects in these layered materials. (c) 2005 Elsevier B.V All rights reserved.