The selective oxidation on InAlAs operated at near-room temperature by liquid phase oxidation using photoresist or metal as a mask is proposed, and further application to In0.52Al0.48As/In0.53Ga0.47As metal-oxide-semiconductor metamorphic high electron mobility transistors (MOS-MHEMTs) is conducted. Besides selective oxidation between oxide film and photoresist or metal, the oxide surface composition for a long oxidation time is also evaluated. Before gate metallization in device fabrication, two commonly used gate recess processes are accessed, and the root mean square value of surface roughness is estimated to be 0.72 and 0.14 nm by the H3PO4-based etchant and the citric acid-based etchant, respectively. As compared to the conventional MHEMT, the fabricated MOS-MHEMT exhibits 4-5 orders of magnitude lower gate leakage, and an improved rf performance. (c) 2007 The Electrochemical Society.