Photoluminescence intensity (PLI) measurements of GaAs and InGaAs thin films indicate that InGaAs might be inherently easier to passivate than GaAs. The introduction of just 15% of In leads to a reduction of the surface recombination velocity at native oxide interfaces by an order of magnitude. This is more than the effect expected by a reduced bandgap alone. The PLI method applied to thin films can also be used to determine the surface recombination velocity of other IIIV-oxide interfaces.