The invention relates to a method of reducing vertical divergence of a high-power semiconductor laser with a negligible threshold current and conversion efficiency penalty. The low divergence is achieved by increasing the thickness of the n-cladding layer in an asymmetric laser diode stack structure, to a value ranging from 1 to 4 times 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 the optical mode, measuring 0.03% or less of the maximal optical power density of said optical mode.