Cuprous halides (CuX) are transparent semiconductors with a range of appealing characteristics, and with targeted applications in electronics, energy storage, and sensing. Here, it is demonstrated that CuX films can be formed at room temperature and atmospheric pressure using a rapid, plasma-based approach. Crystalline CuX products are formed using dielectric barrier discharge plasma to react liquid small-molecule precursors (1,2-dichloro-4-X-benzene, where X = Cl, Br, and I) with a copper substrate via a plasma-assisted reaction. This process produces a composite film, containing both an organic polymer and the cuprous halide crystallites, with a hierarchical nanostructure. The cuprous halides have the zincblende structure, with sizes ranging from ≈10 to ≈85 nm. By employing either neat or mixed precursors, products including CuCl, CuBr, CuCl0.1I0.9, and CuBr0.5I0.5 are accessed. Furthermore, the same process can be used to produce AgI films from the iodated precursor molecule on a silver film, demonstrating the remarkable versatility of this approach. This work reveals a flexible new method to produce these technologically relevant I–VII semiconductor films, which can have applications in sensing, batteries, or photovoltaics.