An exhaust gas treatment apparatus comprises an ammonia absorption system and an ammonia conversion system. The ammonia absorption receives ammonia-containing tail gas generated by a semiconductor process, and removes dust from the tail gas, absorbs and decomposes ammonia gas from the tail gas, converts the ammonia gas into aqueous ammonia, and emits the tail gas without the dust and the ammonia to an external environment. The ammonia conversion system receives the ammonia solution from the ammonia absorption system, and converts it into gaseous ammonia, and then converts the gaseous ammonia to produce liquid ammonia by vaporization and cooling-pressurized liquefaction. After that, the liquid ammonia is purified by a purification system to formed hi-purity liquid ammonia.