The recent discovery of oxygen-enhanced wet thermal oxidation has allowed for the oxidation of various low aluminum content and aluminum-free compound semiconductor alloys that are traditionally difficult to thermally oxidize, including those latticed matched to InP, which are of great importance for telecommunications and other applications. In this work we show that it is possible to form thick insulating oxides on InGaAs layers latticed matched to InP by adding trace amounts (<1%) of oxygen relative to the traditional nitrogen carrier gas used in wet oxidation. Oxidations at various relative oxygen/nitrogen ratios up to 0.7% show that at process temperatures below 500°C the oxidation rate of In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As saturates between 0.3 and 0.5% O<SUB>2</SUB>/N<SUB>2</SUB>. This is due to the balance of the thermodynamically favorable oxidation reaction involving dry O<SUB>2</SUB>, which forms a dense As oxide, and the removal of volatile As from the oxide by the H<SUB>2</SUB> byproduct of the less thermodynamically favorable wet oxidation reaction. At higher process temperatures, above 500°C, this saturation in the growth rate with increasing oxygen content is not seen up to 0.7%, which is likely due to increased As dissociation at higher temperatures reducing the need for the As removal reactions critical at lower temperatures. For all temperatures studied the oxidation reaction is linear, 34 nm/hr and 120 nm/hr for 475°C and 510°C respectively, after an initial time delay before oxide growth. Without added O<SUB>2</SUB> there is no measurable oxide growth. AFM measurements of the oxide surface reveal a decrease in the RMS roughness of the oxide surface from 2.97 nm (475°C) to 2.14 nm (525°C) as the temperature was increased. To increase the growth rate and overall uniformity of the oxide an unpolished silicon cover piece in direct contact with the surface to be oxidized was used. This cover piece provides an overpressure of the volatile species during oxidation in the small volume between the sample surface and the cover piece, greatly increasing the uniformity of the oxide (determined via visual inspection) and growth rate. A sample which had only half its surface covered during oxidation was considerably more uniform, with a 2 order of magnitude lower leakage current in the portion covered during oxidation. This is due in part to the increased thickness (350 nm vs. 210 nm), a direct result of the increased oxidation rate caused by the cover piece. While these oxides are not of sufficient quality for use as a gate oxide in field effect devices, they do show promise for use in isolating and passivating devices. A 350 nm oxide reduces the leakage current density beneath a Au:Ti contact by 4.6 orders of magnitude (to <2x10<SUP>-2</SUP> A/cm<SUP>2</SUP> at a bias of 1 V) relative to directly metalized InGaAs.