Lacking a suitable gate insulator, practical GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) have remained all but a dream for more than four decades. The physics and chemistry of III-V compound semiconductor surfaces or interfaces are problems so complex that our understanding is still limited even after enormous research efforts. Most research is focused on surface pretreatments, oxide formation, and dielectric materials; less attention is paid to the Ill-V substrate itself. The purpose of this article is to show that device physics more related to III-V substrates is as important as surface chemistry for realizing high-performance III-V MOSFETs. The history and present status of III-V MOSFET research are briefly reviewed. A model based on the charge neutrality level is proposed to explain all experimental work he performed on III-V MOSFETs using ex situ atomic-layer-deposited high-k dielectrics. This model can also explain all reported experimental observations on III-V MOSFETs using in situ molecular-beam-expitaxy-grown Ga2O3(Gd2O3) as a gate dielectric. Related perspectives are also discussed to understand III-V MOS capacitance-voltage measurements. (C) 2008 American Vacuum Society.