An electrostatic discharge (ESD) protection device including a silicon controlled rectifier and a diode string arranged along a first direction is provided. The silicon controlled rectifier includes an anode and a cathode disposed separately from each other. The anode and the cathode respectively include doped regions. The doped regions in the anode are arranged along a second direction. The doped regions in the cathode are arranged along the second direction. The first direction intersects the second direction.