Semiconductor laser diodes, particularly high power AlGaAs-based ridge-waveguide laser diodes, are often used in opto-electronics as so-called pump lasers for fiber amplifiers in optical communication lines. To provide the desired high power output and stability of such a laser diode and avoid degradation during use, the present invention concerns an improved design of such a device, the improvement in particular significantly minimizing or avoiding (front) end section degradation of such a laser diode and significantly increasing long-term stability. This is achieved by separating the waveguide ridge into an active main ridge section (4) and at least one separate section (12) located at an end of the laser diode, which may be passive. The separation is provided by a trench or gap (10) in the waveguide ridge. The active waveguide section (4) is at least partly covered by the electrode (6) providing the carriers that does not extend to cover the separate ridge section (12), which thus remains essentially free of carriers injected through said electrode (6). There may be a plurality such separate ridge sections, e.g. two separate ridge sections (12, 212), one at each end of the laser diode, dividing the ridge waveguide into three ridge sections, an active main ridge section (4) in the center and a passive separate ridge section (12, 212) at either end. The trenches (10, 110) between the sections and/or the shape and size of the separate ridge section (s) (12, 212) may be adjusted to act as spatial mode filters.