Semiconductors and the associated methodologies applied to electrochemistry have recently grown as an emerging feld  in energy materials and technologies. For example, semiconductor membranes and heterostructure fuel cells are new technological trend, which difer from the traditional fuel cell electrochemistry principle employing three basic functional  components: anode, electrolyte, and cathode. The electrolyte is key to the device performance by providing an ionic charge  fow pathway between the anode and cathode while preventing electron passage. In contrast, semiconductors and derived  heterostructures with electron (hole) conducting materials have demonstrated to be much better ionic conductors than the  conventional ionic electrolytes. The energy band structure and alignment, band bending and built-in electric feld are all  important elements in this context to realize the necessary fuel cell functionalities. This review further extends to semiconductor-based electrochemical energy conversion and storage, describing their fundamentals and working principles, with  the intention of advancing the understanding of the roles of semiconductors and energy bands in electrochemical devices for  energy conversion and storage, as well as applications to meet emerging demands widely involved in energy applications,  such as photocatalysis/water splitting devices, batteries and solar cells. This review provides new ideas and new solutions to  problems beyond the conventional electrochemistry and presents new interdisciplinary approaches to develop clean energy  conversion and storage technologies.