A transistor having a metal nitride layer pattern, etchant and methods of forming the same is provided. A gate insulating layer and/or a metal nitride layer may be formed on a semiconductor substrate. A mask layer may be formed on the metal nitride layer. Using the mask layer as an etching mask, an etching process may be performed on the metal nitride layer, forming the metal nitride layer pattern. An etchant, which may have an oxidizing agent, a chelate agent and/or a pH adjusting mixture, may perform the etching. The methods may reduce etching damage to a gate insulating layer under the metal nitride layer pattern during the formation of a transistor.