High yields of single-crystalline Ge nanowires (NWs) were synthesized through the thermal decomposition of diphenylgermane (DPG) in the vapor phase of a high boiling point organic solvent. The NWs were single crystal and ranged from 7 to 15 nm and 0.5-10 μm in diameter and length 10 respectively. Catalyst-free growth only occured in areas exposed to the organic vapor, with no growth occurring in the liquid phase. NW growth was fully localizable to surfaces heated within a critical nucleation temperature range. High density, perpendicular arrays of Ge NWs were subsequently grown from 15 ITO coated substrates. This approach represents a viable and convenient route toward orientated arrays of catalyst-free Ge NWs for high-performance device applications. ; peer-reviewed