The present invention discloses a light sensing unit of a light sensing device including a light sensing element and a switching element. The light sensing element includes a gate, a semiconductor layer, a gate insulating layer, a source, and a drain. The gate and the semiconductor layer are disposed on a substrate, the gate insulating layer separates the gate from the semiconductor layer, and the source and the drain are connected to the semiconductor layer respectively. At least one of the source and the drain are formed of a light-transmissive conductive layer. The semiconductor layer is disposed between one of the source and the drain and the gate, and when viewed along a normal direction of the substrate, the gate overlaps the one of the source and the drain, and the gate does not overlap another one of the source and the drain.