A ridge-waveguide semiconductor laser diode with an improved current injection structure is provided. The ridge-waveguide semiconductor laser diode includes: a substrate; a lower multi-semiconductor layer formed on the substrate; an active layer formed on the lower multi-semiconductor layer; an upper multi-semiconductor layer having a ridge portion and formed on the active layer; and an upper electrode formed on the upper multi-semiconductor layer, wherein the upper electrode covers at least one side surface of the ridge portion.