Coplanar wave-guide grounded lines (CPWG) have been designed, realized by micro-machining of high resistivity silicon wafers and tested up to 40 GHz. Different configurations have been compared between them by changing the dimensions of the micro-machined via-holes used for the ground connection, as well as their number and separation, to get the optimal electrical matching conditions. Wide-band matching and losses as low as 0.1–0.2 dB/mm have been obtained within the 40 GHz range, in agreement with the predicted behavior.