Abstract: The invention provides a process for producing a mesoporous single crystal of a semiconductor, wherein the shortest external dimension of said single crystal, measured along any of the crystallographic principal axes of said single crystal, is x, wherein x is equal to or greater than 50 nm, which process comprises growing a single crystal of a semiconductor within a mesoporous template material until said shortest external dimension of the single crystal is equal to or greater than x. Further provided is a mesoporous single crystal obtainable by the process of the invention. The invention also provides a mesoporous single crystal of a semiconductor, wherein the shortest external dimension of said single crystal measured along any of the principal axes of said single crystal is equal to or greater than 50 nm. Further provided is a composition comprising a plurality of mesoporous single crystals of the invention. The invention also provides a semiconducting layer of a mesoporous single crystal of the invention.