Recently, III-V semiconductor nanowires are widely explored as field effect transistor (FET) materials for the next generation high speed electronics. Further tuning the working mode of the nanowire FET is essential in the large scale device design and fabrication, which is still a significant challenging in the current moment. In this study, decoration of metal nanoparticles with different work functions can effectively tune the threshold (VTH) of III-V nanowire FETs. Specifically, high work function metals such as Au and Pt can shift VTH to the positive side while low work function metals such as Al can tune VTH to the negative side, for the typical InAs, InP and InGaAs NWFETs, by depleting electrons from and donating electrons to the III-V nanowire channels. Furthermore, the fabrication of inverters using the depletion and enhancement mode InAs NWFETs show the great potency of the metal decoration method in low-power and high performance electronic devices.