A fuse element, a semiconductor device, and a method for activating a backup unit are provided. The fuse element includes an active area, which includes a source region and a drain region beside the source region, a gate region disposed on the active area, and a shallow trench isolation (STI) structure surrounding the active area. In addition, the drain region includes a terminal configured to receive a stress voltage, such that a conductive path is established through the drain region to the source region.