The invention relates to wavelength stabilization and wavelength multiplexing of multiple high-power multi-mode semiconductor lasers. The lasers are wavelength-stabilized in free space using multi-peak output reflectors to wavelength-lock their output at different reflection wavelength in dependence on operating conditions, to reduce output reflectivity required for locking and increase output power. Selecting output reflectors having different non-overlapping sets of reflectivity peaks for different lasers or groups of lasers enables combining their output by wavelength multiplexing.