In this work, we demonstrate high-performance Enhancement-mode (E-mode) GaN Metal-Oxide-Semiconductor High Electron Mobility Transistors (MOS-HEMTs) on Si substrate based on sidewall depletion achieved by nanostructured gate with large work-function metal. The devices presented threshold voltage (VTH) over 0.6 V at 1 μA/mm, large current density (IDS) up to 590 mA/mm, low specific on resistance (RON,SP) of 1.33 mΩ·cm2, high ON/OFF ratio over 1010 and large breakdown voltage (VBR) of 1080 V at 1 μA/mm with grounded substrate. The excellent high power FOM of 877 MW/cm2 reveals the potential of our approach to obtain E-mode operation, while maintaining exceptional on-state performance and high VBR.