A method for fabricating a semiconductor device includes the steps of: providing a first dielectric layer having a metal layer therein; forming a second dielectric layer on the first dielectric layer and the metal layer; forming a metal oxide layer on the second dielectric layer; performing a first etching process by using a chlorine-based etchant to remove part of the metal oxide layer to forma via opening and expose the second dielectric layer; forming a block layer on sidewalls of the metal oxide layer and a top surface of the second dielectric layer; and performing a second etching process by using a fluorine-based etchant to remove part of the block layer and part of the second dielectric layer for exposing a top surface of the metal layer.