Semiconducting nanowire devices were fabricated using photolithography and e-beam lithography, and their electrical properties were studied. Atmosphere pressure dependent electrical properties of the ZnO nanowire field effect transistor (FET) were studied and its analysis methods with PSPICE simulation were applied to explain the conductance changes in nanowire devices. A single ZnO nanowire FET was fabricated by electron beam lithography and its current-voltage characteristics were recorded with varying the atmosphere pressure to test the possible applications as a chemical gas sensor. Current-voltage characteristics showed typical non-ohmic behaviors, reflecting the influence of the contact barriers formed between the ZnO nanowire FET and metal electrodes. In this paper, an equivalent circuit model of the ZnO nanowire FET is suggested in order to model the contact barriers in nanowire devices, showing that most changes of the electrical conductance might originate from the contact region.