We have attained low leakage current, low interfacial traps, and low border traps by effectively passivating both p- and n-In0.53Ga0.47As (InGaAs) surfaces using the same gate dielectrics of ultra-high-vacuum deposited Al2O3/Y2O3. Gate leakage currents below 2 × 10−7 A/cm2 at gate fields of ±4 MV/cm were obtained after 800 °C rapid thermal annealing, demonstrating the intactness of the interface and heterostructure. Negligibly small frequency dispersions in the capacitance–voltage (C–V) characteristics of p- and n-type metal-oxide-semiconductor capacitors (MOSCAPs) were obtained from accumulation, flatband, to depletion as measured from 300 K to 77 K, indicative of low border and interfacial trap density; the C–V frequency dispersions in the accumulation region are 1.5%/dec (300 K) and 0.19%/dec (77 K) for p-InGaAs, and 2.2%/dec (300 K) and 0.97%/dec (77 K) for n-InGaAs. Very low interfacial trap densities (Dit's) of (1.7–3.2) × 1011 eV−1cm−2 and (6.7–8.5) × 1010 eV−1cm−2, as extracted from the conductance method, were achieved on p- and n-InGaAs MOSCAPs, respectively.