Abstract: A gas supply apparatus for introducing gases to a process chamber of a PECVD system is provided. The gas supply apparatus includes a gas inlet tube, a process gas pipe, a cleaning gas pipe, a remote plasma source (RPS) and a variable valve. The RPS is connected with a cleaning gas source, and the cleaning gas pipe is connected between the gas inlet tube and the RPS for introducing a cleaning gas from the RPS to the gas inlet tube. The process gas pipe is connected between the gas inlet tube and a process gas source for introducing a process gas to the gas inlet tube. The variable valve is installed in the gas inlet tube for closing a passage between the cleaning gas pipe and the gas inlet tube to prevent the process gas entering the cleaning gas pipe when the process gas is introduced to the process chamber.