A semiconductor device, comprising a substrate, a semiconductive layer and a gate electrode is provided. The semiconductive layer having a crystallization promoting material is formed over the substrate. The semiconductive layer has a channel region, a first doped region and a second doped region. The first doped region has a donor and an acceptor, and the second doped region has a dopant which is selected from one of the donor and the acceptor. The second doped region is disposed between the first doped region and the channel region. The gate electrode is insulated from the channel region.