In this work a MEMS gas calibration source will be presented. For reliable and quantitative automatic measures over long periods of time, gas sensors and micro-analytical-systems require periodical calibrations. The authors developed an innovative solution based on a liquid reservoir and silicon micromachined nanochannels. To provide low emission rates of highly volatile substances (e.g. toluene) in the ng/min range, micro-channels have millimetric length, micrometric width and nanometric depth, with a typical cross-section of 0.5 μm2. Prototypal devices with different channel dimensions, shapes and numbers have been built and functionally characterized. Technological fabrication process flow and characterization results will be shown, and the results will be compared with commercially available permeation tubes.