A semiconductor device includes a base substrate, a first thin film transistor disposed on the base substrate, a second thin film transistor disposed on the base substrate, and a plurality of insulating layers disposed on the base substrate. The first thin film transistor includes a first input electrode, a first output electrode, a first control electrode, and a first oxide semiconductor pattern, which are disposed on the base substrate. The second thin film transistor includes a second input electrode, a second output electrode, a second control electrode, and a second oxide semiconductor pattern, which are disposed on the base substrate. The first oxide semiconductor pattern includes a crystalline oxide semiconductor, and the second oxide semiconductor pattern includes an oxide semiconductor having a crystal structure different from a crystal structure of the first oxide semiconductor pattern.