The metal oxide semiconductor thin film gas sensors have been successfully fabricated on a nanospiked silicon surface formed with femtosecond laser irradiations. The sensors show significant response to CO gas at room temperature. It is well-known that the C-O is polarized with positive charges on oxygen atom and negative charges on carbon atom. When the currents pass through the semiconductor sensitive layer, some electrons may accumulate on the tips of the nanospikes to maintain the same electric potential on the surface, which results in strong local electrical fields near the tips of the nanospikes. Then more CO molecules will be pulled onto the tips of the nanospikes and this will enhance the sensitivity of the sensor. A gate bias enhancement has been studied on silicon/oxide layer/semiconductor architecture with the underlying silicon substrate as the back gate. The bias voltage applied on the gate can further enhance the sensitivities of the gas sensors by alternating the electron (or hole) concentration on the surfaces of the metal oxide semiconductor thin film.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.