A transistor structure may include a first electrode, a second electrode, a third electrode, a substrate, and a semiconductor member. The semiconductor member overlaps the third electrode and includes a first semiconductor portion, a second semiconductor portion, and a third semiconductor portion. The first semiconductor portion directly contacts the first electrode, is directly connected to the third semiconductor portion, and is connected through the third semiconductor portion to the second semiconductor portion. The second semiconductor portion directly contacts the second electrode and is directly connected to the third semiconductor portion. A minimum distance between the first semiconductor portion and the substrate is unequal to a minimum distance between the second semiconductor portion and the substrate.