A method for the production of a separation microcolumn made in silicon wafer (11), for a chromatographic or gas-chromatographic system, is described. According to the method, a micro-trench (14) is first made in the silicon wafer. The micro-trench extends in depth in the silicon wafer (11) and along the entire path of the microcolumn. Then, a perfectly circular micro-channel (20), tangent to the upper surface of the silicon wafer (11), is obtained by an in-depth isotropic etching with reactive ions in the micro-trench (14). The microcolumn is ...