A method of synthesis of two-dimensional metal chalcogenide monolayers, such as WSe2 and MoSe2, is based on a chemical vapor deposition approach that uses H2Se or alkyl or aryl selenide precursors to form a reactive gas. The gaseous selenium precursor may be introduced into a tube furnace containing a metal precursor at a selected temperature, wherein the selenium and metal precursors react to form metal chalcogenide monolayers.