0_6720 The Rashba interaction can give rise to prominent spin-dependent effects in the surface electronic structure of Bi-containing nano-systems, owing to the large atomic spin-orbit coupling of Bi and the broken translational symmetry. Here, we report on the electronic properties of the (2×1) phase of Bi on the InAs(100) surface analyzed by spin- and angle-resolved photoemission spectroscopy, scanning tunneling spectroscopy and density functional theory. The system consists of Bi dimer lines running along the [011] direction of the substrate. Two pairs of spin-split bands are observed experimentally near the Fermi level. The pair located at larger in-plane momenta displays open wavy contours on constant energy planes and giant Rashba parameter. The inner bands have straight (open) or oval (closed) contours depending on their spin, resulting in a spin imbalance close to the Fermi level. These findings allow us to describe the system as a quasi-one-dimensional metal monolayer/semiconductor interface with exceptionally large Rashba interaction and topological-like spin texture.