A horizontal p?i?n ridge waveguide emitter on a silicon (100) substrate with a Ge0.91Sn0.09/Ge multi-quantum-well (MQW) active layer was fabricated by molecular beam epitaxy. The device structure was designed to reduce light absorption of metal electrodes and improve injection efficiency. Electroluminescence (EL) at a wavelength of 2160 nm was observed at room temperature. Theoretical calculations indicate that the emission peak corresponds well to the direct bandgap transition (n1Γ?n1HH). The light output power was about 2.0 μW with an injection current density of 200kA/cm2. These results show that the horizontal GeSn/Ge MQW ridge waveguide emitters have great prospects for group-IV light sources.