SnO2-ZnO composite nanofibers have been fabricated on Si/SiO2/Ti/Pt substrates by a novel method named as "stepwise-heating electrospinning'' in this paper. The Si/SiO2/Ti/Pt substrates were fabricated by typical MEMS technology including some technological processes of thermal oxidation, photolithography, sputtering, and liftoff. Comparing with normal ceramic tube sensor fabrication process, spin coating or grinding was not needed during the sensors fabrication using silicon planar technology, which avoided destroying the original morphologies of nanomaterials. The ZnO-modified SnO2 shows good sensing properties to methanol due to the presence of N-N heterojunction at the interface of ZnO and SnO2 grains. The efficient charge separation of SnO2-ZnO heterojunction in the gas sensing performance was discussed from the perspective of energy band and formation of electronic accumulation layer as well as depletion layer. A detailed description of the change of band bending and potential barrier height of SnO2-ZnO composite nanofibers was also given, as well as a specific sensing mechanism in the process of methanol adsorption and desorption.