Dilute solutions of (NH4)2S in water and of 1-eicosanethiol (ET) in ethanol were used to deposit a protective layer to prevent the reoxidation of clean In0.53Ga0.47As(100) substrates. The surface composition of the InGaAs after oxide etching in 0.3 M HF, and after immersion in (NH4)2S or ET solutions was studied using XPS. Immersing clean InGaAs substrates in 4.0 mM ET for 20 h protected the surface for 4 min, after which oxide states were detected by XPS. A 20 min immersion in 3 mM (NH4)2S in a glove box slowed down the reoxidation process. After 1 h of atmosphere exposure, the amount of InGaAs oxides on the surface treated in (NH4)2S were lower than those of a control sample after only 4 min of air exposure. The sulfur layer deposited from aqueous ammonium sulfide and the self-assembled eicosanethiol layer blocked reoxidation and chemically passivated the surface only for brief ambient exposures.