We propose and analyze a beam-shaping mechanism that in broad-area semiconductor amplifiers occurs due to spatial pump modulation on a micrometer scale. The study, performed under realistic parameters and conditions, predicts a spatial (angular) filtering of the radiation, which leads to a substantial improvement of the spatial quality of the beam during amplification. Quantitative analysis of spatial filtering performance is presented based on numerical integration of the paraxial propagation model and on analytical estimations.