[en] A fast, simple procedure is described for obtaining an assembly of silver sulfide nanoparticles (Ag₂S NPs) on a glass substrate through reaction of a template of an assembled layer of silver nanoparticles (Ag NPs) with hydrogen sulfide (H₂S) gas. The Ag NP template was prepared by assembling a monolayer of spherical Ag NPs (mean diameter of 7.4 nm) on a polyethylenimine-treated glass substrate. Exposure to pure H₂S for 10 min converted the Ag NPs of the template to Ag₂S NPs. The resulting Ag₂S NP assembly, which retains the template nanostructure and particle distribution, was characterized by optical absorption spectroscopy, atomic force microscopy, transmission electron microscopy (TEM), scanning high resolution TEM, energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. The Ag₂S NPs have a crystal structure of monoclinic acanthite, and while they retained the spherical shape of the original Ag NPs, their mean particle size increased to 8.4 nm due to changes to the crystal structure when the Ag NPs are converted into Ag₂S NPs. The measured optical absorption edge of the Ag₂S NP assembly indicated an indirect interband transition with a band gap energy of 1.71 eV. The Ag₂S NP assembly absorbed light with wavelengths below 725 nm, and the absorbance increased monotonically toward the UV region.