A micro fluidic device includes a valve/pump-unit with reduced dead volume having a substrate. The lower surface of the substrate includes two micro channels spaced apart by a valve area of the substrate that separates the two micro channels. A flexible membrane is arranged on the lower surface of the substrate facing an actuating element located in a through going cut-out of a cover element. Movement of the actuating element towards and away from the valve area of the substrate causes a pump and/or valve action of the flexible membrane area, respectively, to cause or stop a directed fluid flow between the two micro channels through a channel formed between the valve area of the substrate and the flexible membrane.