This invention is directed a method for producing an ultra-high purity semiconductor gas such as ammonia gas. The method includes the steps of directing an ammonia fluid having a liquid phase moisture content that is less than about 500 parts per million through an evaporation means, to produce purified vapor phase ammonia, and directing the purified vapor phase ammonia through an adsorption means to remove impurities therein and produce ultra-high purity ammonia gas.