Electrostatic discharge (ESD) structures are provided. An ESD structure includes a semiconductor substrate, a first epitaxy region with a first type of conductivity over the semiconductor substrate, a second epitaxy region with a second type of conductivity over the semiconductor substrate, and a plurality of first semiconductor layers and a plurality of second semiconductor layers. The first semiconductor layers and the second semiconductor layers are alternatingly stacked over the semiconductor substrate and between the first and second epitaxy regions. Each of the first and second semiconductor layers has a first side contacting the first epitaxy region and a second side contacting the second epitaxy region, and the first side is opposite the second side.