In this work, we demonstrate high-performance Enhancement-mode (E-mode) GaN Metal-Oxide-Semiconductor High Electron Mobility Transistors (MOS-HEMTs) on Si substrate achieved by a nanostructured gate region in combination with a large work-function gate metal. Nanowire sidewalls depletion led to a threshold voltage (VTH) positive shift of 4 V with respect to the planar reference, followed by an additional contribution from the large Platinum gate metal work-function to reach full E-mode operation. A careful design of the nanostructured gate allowed for on resistance (RON) and current density (IDS) degradation with respect to planar devices while it significantly increased the breakdown voltage (VBR) by over 40%. The devices presented positive VTH of 0.64 V at 1 μA/mm, low specific on resistance (RON,SP) of 1.33 mΩ·cm 2 , large IDS up to 590 mA/mm, high ON/OFF ratio over 10 10 and large VBR over 1050 V at 1 μA/mm with grounded substrate, resulting in excellent high power FOM of 877 MW/cm 2 . These results unveil the potential of nanostructures to obtain E-mode operation, while maintaining exceptional on-state performance and high VBR.