A semiconductor structure includes a first source/drain region, a second source/drain region, a channel doping region, a gate structure, a first well and a second well. The second source/drain region is disposed opposite to the first source/drain region. The channel doping region is disposed between the first source/drain region and the second source/drain region. The gate structure is disposed on the channel doping region. The first well has a first portion disposed under the first source/drain region. The second well is disposed opposite to the first well and separated from the second source/drain region. The first source/drain region, the second source/drain region and the channel doping region have a first conductive type. The first well and the second well have a second conductive type different from the first conductive type.