A semiconductor structure includes a gate structure, a source region, a drain region, and an isolation structure. The gate structure includes a first portion, a second portion and a third portion. The first portion extends in a first direction, and the second portion and the third portion extend in a second direction. The second portion and the third portion are disposed at opposite ends of the first portion. The source region and the drain region are separated by the gate structure. The isolation structure surrounds the gate structure, the source region and the drain region. The first portion has a first sidewall, the second portion has a second sidewall, and the third portion has a third sidewall. The first sidewall, the second sidewall and the third sidewall are parallel to the first direction and aligned with each other to form a straight line.