A method for fabricating a semiconductor device is provided. A substrate having a dummy gate thereon is prepared. A spacer is disposed on a sidewall of the dummy gate. A source/drain region is disposed adjacent to the dummy gate. A sacrificial layer is then formed on the source/drain region. A cap layer is then formed on the sacrificial layer. A top surface of the cap layer is coplanar with a top surface of the dummy gate. A replacement metal gate (RMG) process is performed to transform the dummy gate into a replacement metal gate. An opening is then formed in the cap layer to expose a top surface of the sacrificial layer. The sacrificial layer is removed through the opening, thereby forming a lower contact hole exposing a top surface of the source/drain region. A lower contact plug is then formed in the lower contact hole.