An electrostatic discharge (ESD) device includes a substrate, an external well of a first conductivity type in the substrate, and an internal well of a second conductivity type in the external well, the first conductivity type opposite the second conductivity type. The ESD device further includes a first heavily doped region of the first conductivity type located at a surface of the internal well, a second heavily doped region of the second conductivity type located at a surface of the internal well, and a third heavily doped region of the first conductivity type located at a surface of the external well. The second heavily doped region is interposed between and spaced from each of the first and third heavily doped regions, and at least one of a space between the first and second heavily doped regions and a space between the second and third heavily doped regions is devoid of a device isolation structure of electrical isolation material.