A substrate processing apparatus includes a process chamber including a plasma generation region configured to receive at least one first process gas and have first radio-frequency (RF) power applied thereto, to generate plasma; a gas distribution region configured to supply the at least one first process gas to the plasma generation region; a gas mixing region configured to receive at least one second process gas and radicals generated in the plasma generation region to generate an etchant based on the radicals being mixed with the at least one second process gas; a pedestal on which a substrate is disposed; a processing region in which the pedestal is installed; and a shower head configured to supply the etchant from the gas mixing region to the processing region, the substrate disposed on the pedestal being processed by the etchant. The gas mixing region is separate from each of the plasma generation region and the processing region.