A method of producing a III-V fin structure within a gap separating shallow trench isolation (STI) structures and exposing a semiconductor substrate is disclosed, the method comprising providing a semiconductor substrate, providing in the semiconductor substrate at least two identical STI structures separated by a gap exposing the semiconductor substrate, wherein said gap is bounded by said at least two identical STI structures, and, producing a III-V fin structure within said gap on the exposed semiconductor substrate, and providing a diffusion barrier at least in contact with each side wall of said at least two identical STI structures and with side walls of said III-V fin structure and wherein said semiconductor substrate is a Si substrate.