The impact of La<inf>2</inf>O<inf>3</inf>/InGaAs MOS interfaces on the performance of InGaAs MOSFETs and the physical origins are systematically investigated. It is found that La<inf>2</inf>O<inf>3</inf>/ InGaAs MOSFETs exhibit lower S. S. and lower carrier trapping properties, while have lower mobility than Al<inf>2</inf>O<inf>3</inf>/ InGaAs MOSFETs because of higher fixed oxide charge density. Also, it is experimentally found for the first time that ALD La<inf>2</inf>O<inf>3</inf> films with thermal budget lower than 300°C have ferroelectricity in W/La<inf>2</inf>O<inf>3</inf>/InGaAs MOS and W/La<inf>2</inf>O<inf>3</inf>/W MIM structures. The steep slope characteristics due to the negative capacitance (NC) effect have been demonstrated for the first time in W/La<inf>2</inf>O<inf>3</inf>(15nm)/InGaAs MOSFETs.