An apparatus and method for treating a semiconductor process gas comprises a gas inlet allowing a treatment target gas (or gas to be treated) to flow therethrough; a catalytic reaction portion including a catalyst and configured to allow the treatment target gas to be brought into contact with the catalyst; a space velocity controller between the gas inlet and the catalytic reaction portion, the space velocity controller extending from the gas inlet in a diagonal direction in relation to the gas inlet; a differential pressure buffer portion between the space velocity controller and the catalytic reaction portion and including a filter; and a gas outlet configured to externally discharge a product formed as the treatment target gas comes into contact with the catalyst.