LaFeO3, La1-xSrxFeO3 (x=0.1, 0.2 and 0.4) and LaFe1-yCoyO3 (y=0.1, 0.2, 0.3, 0.4, 0.6 and 1.0) nanocrystalline thin frlms were fabricated on monocrystalline silicon wafers by a new sol-gel method with microtechnology. The XRD and SEM studies of the samples showed that the doping of the Sr2+ and Co3+ ions in LaFeO3, substituting for La3+ and Fe3+ ions, respectively, has different effects on the solid state reaction and the average grain size of the thin films obtained. We have tried to manufacture a new type NCTF-OSFET gas sensing device for the first time, in which the aluminum gate was replaced by LaFeO3 nanocrystalline thin films (NCTF) combined with the planar technique of integrated circuits, and the results are satisfactory. This device not only has an excellent selectivity to ethanol, but also has a good sensitivity.