The invention relates to a method of reducing vertical divergence of a high-power semiconductor laser with a negligible generated threshold current and conversion efficiency loss. The low divergence is achieved by increasing the thickness of the n-cladding layer in an asymmetric laser diode stack structure, with a value ranging from 1 to 4 times higher than the laser mode size measured at 10% level. The divergence may be tuned by adjusting the n-cladding layer parameters in an area of the tail of the optical mode, the measured optical power density of the area of the tail is 0.03% or less of the maximal optical power density of the optical mode.