The present invention relates to a chromatographic separation device comprising a first substrate body carrying a micro-fabricated separation channel recessed on one of its surfaces and covered by a second substrate body, both perforated with connection-holes for the supply and withdrawal of a sample and carrier liquid. The present device is characterized in that said micro-fabricated separation channel is preceded or succeeded by a flow distribution region that is filled with an array of micro-fabricated pillars, having a shape, size and positioning pattern selected such that said flow distribution region has a ratio of transversal to axial permeability of at least 2.