Iranian researchers succeeded in the synthesis of zinc sulfide nanoparticles with dimension of 21 nm through hydrothermal method. The product is semi-conductor and can be used in optics, photo-electronics, sensors, catalysts, and so on. Nano-crystalline of metals, metal oxides, and semi-conductors are very popular due to their unique mechanical, electrical, optical, magnetic, and chemical properties. The reason is quantum effects, to the extent that electrical, optical, and other properties are highly dependent on particle size at small dimensions. Dr. Maryam Mohammadi Kish, an assistant professor in inorganic chemistry from Kharazmi University of Tehran, elaborated on the research, and stated, “The main objective of this research was to synthesize zinc sulfide at nanometric scale, and to optimize the synthesis method by comparing various temperatures and times, and finally to determine the band gap of the products. Size control is one of the most important parameters in the synthesis of semi-conductors. However, the most important parameter is particle size distribution. In this research, nanoparticles were synthesized at 21 nm with appropriate size distribution.” Among various methods, hydrothermal method is an appropriate one for the synthesis of nanoparticles due to its low cost, high performance, and the ability to be used at large scale. Among the advantages of this research, mention can be made of the use of simple initial material, appropriate temperature and time conditions, and simple laboratory facilities. One of the results of the research was the application of hydrothermal method to synthesize zinc sulfide nanoparticles with dimension of 21 nm. The product is an II-IV semi-conductor with a direct band gap of 3.65-3.87 eV. Results of the research have been published in details in April 2013 in Ceramics International, vol. 39, issue 3, pp. 3173-3181.