A biological device includes a substrate, a gate electrode, and a sensing well. The substrate includes a source region, a drain region, a channel region, a body region, and a sensing region. The channel region is disposed between the source region and the drain region. The sensing region is at least disposed between the channel region and the body region. The gate electrode is at least disposed on or above the channel region of the substrate. The sensing well is at least disposed adjacent to the sensing region.