Proximity phenomena between superconductors and topological semimetals are at the heart of the search for novel quantum states of matter. Here we show that the epitaxial interface between one-to three-atomic-layer Pb and the Sb(111) substrate has extremely high electronic transparency. As a result, Pb loses its superconducting and even its metallic properties; its electronic spectrum mimics the semimetallic density of states of Sb. Additional states arise from a threefold symmetric potential which develops at the Pb/Sb interface. Our experimental results are supported by DFT simulations which demonstrate that this potential arises from the corrugated structure of the Pb/Sb interface.