In some embodiments, an electrostatic discharge (ESD) protection circuit includes a substrate resistance control circuit coupled to a body of a first NMOS transistor. The substrate resistance control circuit increases a resistance of the body of the first NMOS transistor during an ESD event. The first NMOS transistor has a drain coupled to an input/output (I/O) pad and a gate coupled to a first voltage source. The first voltage source is set at ground potential.