A semiconductor structure and an electrostatic discharge protection circuit are disclosed. The semiconductor structure includes a device structure comprising a first well region, a second well region, a source, a drain, an extending doped region, and a gate structure. The second well region has conductivity type opposite to a conductivity type of the first well region. The drain has a conductivity type same as a conductivity type of the source. The source and the drain are formed in the first well region and the second well region respectively. The extending doped region is adjoined with drain and extended under the drain. The extending doped region has a conductivity type same as the conductivity type of the drain. The gate structure is on the first well region.