A nanosensor and microsensor fabrication method employing scanning probe microscopy (SPM) is demonstrated. Within such process, nano- or microscale metal oxide (MoOx or TiOx) structures, constituting the active region of a sensor, are directly fabricated onto a microscopic metal track via SPM-assisted local anodic oxidation (LAO). Two distinct LAO routes, a slow (conventional) or a fast (unusual) one, are employed to produce nano- and microsensors, which are tested at different temperatures using CO2 and H-2 as test gases. Sensitivities down to ppm levels are demonstrated, and the possibility of easy integration into microfabrication processes is also discussed.