An electrostatic discharge (ESD) protection circuit includes a field oxide device in a substrate, wherein the field oxide device is coupled between an input/output (I/O) pad and a first terminal. The field oxide device includes a drain end and a source end having a first type of dopant. The field oxide device includes a field oxide structure between the drain end and the source end. The field oxide structure has a top surface co-planar with a top surface of a substrate. A first doped region having a second type of dopant is adjacent to the drain end. A second doped region having the second type of dopant is adjacent to the source end. The field oxide structure is in a well and the source end and the drain end are separate from the well. The substrate has the second type of dopant and is around the field oxide structure.
