A method for fabricating semiconductor device includes the steps of: forming a first metal interconnection in a first inter-metal dielectric (IMD) layer; performing a treatment process to rough a top surface of the first metal interconnection; and forming a carbon nanotube (CNT) junction on the first metal interconnection. Preferably, the treatment process further includes forming protrusions on the top surface of the first metal interconnection, in which the protrusions and the first metal interconnection comprise same material.