Large channel length field effect transistors (FETs) based on Pt contacts to ferromagnetic BiMn-codopedZnO bicrystal nanobelts have been fabricated using dielectrophoresis and a focused ion beam. Electricaltransport studies show n-type behavior of the ferromagnetic ZnO nanobelts. The current−voltage characteristicsof the FETs exhibit Schottky barrier behavior. The contact resistances and the Pt diffusion are responsible forthe reduction of the conductance and the threshold shift. The reduction of the mobility can be attributed tothe enhanced interface scattering at Pt electrodes/nanobelt contact regions after Pt deposition. The devicesare also found to be strongly dependent on the channel length.