Single-crystalline germanium nanowires were synthesized via vapor-liquid-solid mechanism. The characteristics of the Ge nanowires were investigated by a transmission electron microscope to identify the  growth direction. The Ge nanowire-based field-effect-transistors on Si 3N 4 dielectrics were fabricated, showing a p-type semiconducting behavior with hole mobility of 47.03 cm 2 V -1 s -1. The formation of Cu 3Ge/Ge/Cu 3Ge nanoheterostructures was demonstrated with the reaction between copper contacts and Ge nanowires by rapid thermal annealing. The diameter-dependent electrical transport property of Ge nanowires indicates that with diameters of more than 80 nm, the resistivity of Ge nanowires decreased with diameter decrease, while with diameters of less than 80 nm, it increased. With multiple annealing processes, the channel length of the Ge nanowire transistors can be successfully controlled. From electrical measurements of each annealing step, the electrical transport property was significantly improved by sequential formation of Cu 3Ge contacts. The gradual formation of the germanide structure reduces Fermi level pinning effect and increases the Ohmic behavior of electrical transportation.