A method for fabricating semiconductor device includes the steps of first bonding a top wafer to a bottom wafer, performing an edge trimming process to remove part of the top wafer, forming a pad layer on the top wafer, performing a first etching process to remove part of the pad layer to form a bonding pad, forming a first passivation layer on the bonding pad, and then performing a second etching process to remove part of the first passivation layer.