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An innovative fabrication method to produce a nanoporous Si or SiO2 surface by employing anodic aluminum oxidation (AAO) method and reactive ion beam (RIE) etch of MEMS process is presented. To enhance sensitivity and reduce the sensing dimensions of a gas sensor, a nanoporous surface of gas-sensitive material is preferred. This class of sensor devices can be implemented on silicon or silicon-on-insulator (SOI) substrates that feature a thin membrane of micro-hotplate structure with micro-heaters and electrodes, and operate as chemoresistive devices fabricated by CMOS standard process. Being different from conventional CVD process, PVD-based TiO2 thin films are employed as active layers and deposited onto the AAO-fabricated silicon dioxide porous surface. In this paper an integrated process to fabricate the sensor structure and TiO2 thin film deposition are developed, and comprehensive gas tests also demonstrate successful results in better sensitivity and faster response time less than 2 min within 4000~6000 ppm of oxygen. Using novel AAO process to fabricate nanoporous gas sensors not only reduces the complexity of conventional surface poration process, but also enhances response performance of gas-sensitive thin films, disclosing a very promising method to produce nanoporous gas sensors in a cost-effective way.