Thick trioctylphosphine oxide (TOPO) layers were controllably coated onto CdTe nanowires. The shell thicknesses were readily tuned by controlling the reaction temperatures in coordinating TOPO solvent or by varying amounts of TOPO in noncoordinating ODE solvent. The shells were coherent and rough if synthesized in the TOPO solvent, while the shells became very uniform and smooth if synthesized in the ODE solvent. The electrically insulating effects of TOPO shells were directly confirmed through nanodevice of individual core/shell nanowire (NW). The present scheme to overcoat TOPO around semiconductor NWs could, in principle, be exploited to be a general approach to encapsulate a variety of colloidal nanocrystals to form novel core-shell nanohybrids.