We report a very simple, robust, and reliable on-chip fabrication method of a chemoresistive sensor based on silicon nanowires(NWs). Our method permits the use of nanowires without the need of their removal and transfer to a support different from the growth substrate. Our method, completely based on the silicon technology platform, exploits nanowires directly grown onto a selected area, over and between pre-patterned, interdigitated electrodes defined on oxidized silicon. The fabricated sensor is capable to detect NO 2 down to a few ppb levels operating at room temperature. The sensor characteristics benefit of the presence of self-welded nanowires.