A self-planarizing Au metallization process by selective electrolytic plating was developed for metal interconnections in the submicron range. This process is superior to the conventional gold metallization process and economically viable due to its simplicity and no use of ion-milling. The reaction mechanism of the selective plating between metal and semiconductor electrodes was studied. Voltammetry showed that a much higher deposition potential is required for an oxidized TiW electrode than that for an Au electrode. In this paper, we use the existing TiW barrier layer as part of the electrode during Au plating. Through an O-2 plasma treatment, which is an exiting step for photoresist ashing, we turn the TiW electrode from metallic into semiconducting. Under optimized electrolytic plating conditions, we can selectively plate Au wires into dielectric trenches while leaving the oxidized TiW field free of Au.