A display device may include a substrate, a buffer layer on the substrate, a first active pattern on the buffer layer, the first active pattern having a first thickness, a second active pattern on the buffer layer spaced from the first active pattern and having a second thickness smaller than the first thickness, a first gate insulating layer on the first active pattern and the second active pattern, a first gate electrode on the first gate insulating layer, the first gate electrode overlapping the first active pattern, and a second gate electrode on the first gate insulating layer, the second gate electrode overlapping the second active pattern.