The fabrication process of a novel Si interface control layer (Si ICL)-based oxide-free insulated gate structure for InP metal-insulator-semiconductor field effect transistors (MISFETs) was successfully characterized and optimized using in-situ reflection of high-energy electron diffraction (RHEED), Raman scattering spectroscopy, X-ray photoelectron spectroscopy (XPS) and capacitance-voltage (C-V) techniques, and applied for fabrication of MISFETs. RHEED observation indicated that the optimum initial thickness of the Si ICL with single crystal pseudomorphic growth of Si on InP is 10 . Raman scattering spectroscopy showed existence of surface strain on InP covered with the Si ICL without changing LO-phonon peak width, indicating that the Si ICL is grown in a pseudomorphic fashion. A detailed XPS analysis showed that Fermi level pinning was largely reduced by the growth of the Si ICL and its partial electron cyclotron resonance (ECR) plasma nitridation realizing an optimum Si ICL thickness of 5 with a good interface to SiNx. C-V measurement confirmed that the optimum Si ICL-based gate formation process realized a full swing of Fermi level almost over the entire bandgap. The fabricated MISFET using the optimum gate structure exhibited excellent gate controllability and stable operation with a low gate leakage currents.