A micromachined miniature valve used for gas chromatography has very low valve and interconnection dimensions to reduce the fluid volume inherent in other gas switching valves to thereby provide accurate measurements involving small gas flows. In order to reduce actuating diaphragm size, without encountering excessive stress concentrations in the diaphragm, the diaphragm can be polyimide film actuated in connection with a silicon valve body having valve seats with ports that are opened or closed by deflection of the diaphragm. Silicon wafers can be micromachined using batch fabrication techniques to provide the necessary valve seats and passageways for operating. The valve assembly is produced as a layered sandwich made up of individual wafers, including an actuator layer, a stop layer, a valve seat layer, and a layer which has flow channels receiving gas from the valve seat layer and making the necessary interconnections to provided outlets. The diaphragm film is positioned between the valve seat layer and the stop layer, and is deflected or displaced to control passage of gases through the valve openings. The diaphragm layer is sealed to the silicon valve body by a process which involves fusing, such as glass frit or solder sealing.