High mobility InxGa1-xAs material is one of the most promising candidates as channel material for post CMOS device applications. In this presentation, InxGa1-xAs material based MOS capacitors will be studied for possible applications for future III-V MOSFET, TFET and FINFET devices. To improve the gate leakage of the InxGa1-xAs MOSCAP, the combination of wet chemical treatment and in-situ trimethyl aluminum (TMA) pretreatment was found to be the most effective method for InxGa1-xAs surface cleaning to achieve a fully inverted InxGa1-xAs MOSCAP for post CMOS digital applications. In addition, a high-k composite oxide composed of La2O3 and HfO2 is investigated for InxGa1-xAs metal-oxide-semiconductor (MOS) capacitor application. The composite oxide was formed by depositing five layers of La2O3(0.8 nm)/ HfO2(0.8 nm) on InxGa1-xAs with post deposition annealing at 500 °C. The MOS capacitors fabricated show good inversion behavior, high capacitance, low leakage current, with excellent interface trap density (Dit) of 7.0 × 1011 cm-2eV-1, small hysteresis of 200 mV and low capacitance equivalent thickness of 2.2 nm at 1 kHz were also achieved.