A method for forming a miniature skimmer cone for a free jet expansion vacuum interface is disclosed. The skimmer cone is formed from electroplated metal, deposited inside a blind hole formed on a silicon substrate. The substrate is partially removed to expose the skimmer cone, together with other features formed by etching, and an outlet orifice is formed. A complete miniature vacuum interface is formed from the stacked assembly of a part containing an inlet orifice, a spacer, and the part containing a skimmer cone described above, mounted in an intermediate pressure chamber at the inlet to a mass spectrometer.