Abstract: A metal-oxide-semiconductor (MOS) transistor having a gate electrode comprising a metal oxynitride and a method of forming the same are provided. The metal oxynitride preferably comprises molybdenum oxynitride and/or iridium oxynitride. The gate electrode may further comprise carbon and/or silicon. The gate electrode is preferably formed in a chamber containing nitrogen, oxygen and a carbon-containing gas. The gate electrode of the MOS transistor has a high work function and a low equivalent oxide thickness.