The authors report the self-assembly and characterization of monolayer PbS quantum dots (QDs) on GaAs substrates and the effect of thermal annealing on close-packed PbS QD films. The QD monolayer film was prepared using a 1,6-hexanedithiol self-assembled monolayer to link PbS QDs to GaAs substrates. Atomic force microscopy measurement confirmed the formation of PbS QD monolayer on GaAs. The temperature dependence of photoluminescence (PL) intensity of PbS QDs shows a feature typical for close-packed PbS QD films. For investigation of the influence of thermal annealing, three close-packed films of colloidal PbS QDs were prepared by drop coating and treated at different annealing temperatures. By controlling the annealing temperature, the PL intensity of close-packed films at room temperature can be improved. The room temperature PL intensity can be adjusted to be higher than that at 10 K. These results provide insights for future applications of colloidal QDs and the improvement of their performances. (C) 2010 American Vacuum Society. [DOI:10.1116/1.3456172]