A semiconductor nanoparticle, a production method thereof, and an electroluminescent device including the same. The production method includes: combining a magnesium precursor and an additive with a chalcogen precursor in a reaction medium including an organic solvent and an organic ligand; heating the reaction medium to a reaction temperature; and reacting the magnesium precursor and the chalcogen precursor in the presence of the additive to form a magnesium chalcogenide, wherein the semiconductor nanoparticle comprises the magnesium chalcogenide, wherein the magnesium chalcogenide comprises magnesium; and selenium, sulfur, or a combination thereof, and wherein the additive includes a hydride compound including an alkali metal, calcium, barium, aluminum, or a combination thereof.