the invention relates to a method of purifying a fluoride in a semiconductor process waste gas . the method comprises the steps of importing a mist gaseous water at a high temperature produced by heating water in a reaction chamber of a semiconductor waste gas treating tank ; and dissolving the fluoride into a hydrogen fluoride by using the mist gaseous water , wherein a dissolving temperature of the mist gaseous water contacting with the fluoride is 370 ˜ 1300 ° c . this invention provides a device of purifying a fluoride in a semiconductor process waste gas . the conventional problems saying that the steps and structure of the device of purifying the fluoride in the semiconductor process waste gas are too complex and a purifying efficiency is hard to be increased .