An active device includes a poly-silicon semiconductor layer, a first insulating layer, a gate electrode, a second insulating layer, a first through hole, an oxide semiconductor layer, a first electrode and a second electrode. The poly-silicon semiconductor layer includes a first doped region, a channel region and a second doped region. The gate electrode is disposed on the first insulating layer covering the poly-silicon semiconductor layer, and corresponds to the channel region. The gate electrode is covered by the second insulating layer, where the first and second insulating layers have a first through hole. The oxide semiconductor layer is disposed on the second insulating layer and corresponds to the gate electrode. The first and second electrodes are oppositely disposed on the oxide semiconductor layer. The oxide semiconductor layer is electrically connected to the second electrode, and to the second doped region via the first through hole.