Si complementary metal-oxide-semiconductor (CMOS) technology has been prospered through continuously scaling of its feature size. As scaling is approaching its physical limitations, new materials and device structures are expected. High electron mobility III-V materials are attractive as alternative channel materials for future post-Si CMOS applications due to their outstanding transport property. High-k dielectrics/metal gate stack was applied to reduced gate leakage current and thus lower the power dissipation. Combining their benefits, great efforts have been devoted to explore III-V/high-k/metal metal-oxide-semiconductor field-effect-transistors (MOSFETs). The main challenges for III-V MOSFETs include interface issues of high-k/III-V, source and drain contact, silicon integration and reliability. A comprehensive study on III-V MOSFETs has been presented here focusing on three areas: 1) III-V/high-k/metal gate stack: material and electrical properties of various high-k dielectrics on III-V substrates have been systematically examined; 2) device architecture: device structures from planar surface channel MOSFETs and buried channel quantum well FETs (QWFETs) to 3D gate-wrapped-around FETs (GWAFETs) and tunneling FETs (TFETs) have been designed and analyzed; 3) fabrication process: process flow has been set up and optimized to build scaled planar and 3D devices with feature size down to 40nm. Potential of high performances have been demonstrated using novel III-V/high-k devices. Effective channel mobility was significantly improved by applying buried channel QWFET structure. Short channel effect control for sub-100nm devices was enhanced by shrinking gate dielectrics, reducing channel thickness and moving from 2D planar to 3D GWAFET structure. InGaAs TFETs have also been developed for ultra-low power application. This research work demonstrates that III-V/high-k/metal MOSFETs with superior device performances are promising candidates for future ultimately scaled logic devices. / text