Abstract: A residual gas removing device for a gas supply apparatus in a semiconductor fabricating facility, includes a low stress valve disposed between a mass flow controller and a chamber. The low stress valve alternately supplies or cuts off a gas from the mass flow controller to the chamber. A WF6 gas removing apparatus is in flow communication with a gas inlet line of the low stress valve to remove a residual WF6 gas in the gas inlet line, before proceeding with a subsequent deposition step.