We present real time conductivity and optical absorption measurements during the reaction of sulfur anions and silver cations. The S^-2 and Ag⁺ are shown to react and form silver sulfide, Ag₂S, semiconductor nanoparticles. Scanning tunneling spectroscopy (STM) and scanning tunneling spectroscopy (STS) measurements are consistent with nanoparticles smaller than 50 nm with a band gap of about 0.90 eV. The kinetics measurements reveal that the rate law is directly proportional to the S^-2 concentration while it is inversely proportional to Ag⁺ concentration. Experimental measurements performed at low temperatures reveal that silver nanoparticles are important intermediates in silver sulfide synthesis. A mechanism for the formation of the Ag₂S nanoparticles that involves Ag nanoparticles intermediates is discussed. Theoretical calculations for the formation of Ag₂S and silver nanoparticles are consistent with steric requirements for the formation of the semiconductor. These steric restrictions are not observed in silver nanoparticle formation.