Abstract: A gas exhaust system for use in a semiconductor manufacturing process wherein mechanical or chemical processing is applied on silicon wafers or the like arranged in a air-tight process chamber thereof, comprises a vacuum chamber having a gas suction port formed on an upper side thereof and a gas exhaust port formed on a lower side thereof. In the vacuum chamber, the first and second rotors are arranged vertically and supported rotatably at their lower end port ions in a cantilevered condition. The first and second rotors are driven to rotate in the opposite directions to thereby form a certain degree of vacuum condition in the vacuum chamber, whereby the residual gasses in the process chamber are discharged therefrom through the gas exhaust system.