A display device includes: a first substrate; a photo transistor on the first substrate; and a switching transistor connected to the photo transistor. The photo transistor includes a light blocking film on the first substrate, a first gate electrode on the light blocking film and in contact with the light blocking film, a first semiconductor layer on the first gate electrode and overlapping the light blocking film, and a first source electrode and a first drain electrode on the first semiconductor layer. The switching transistor includes a second gate electrode on the first substrate, a second semiconductor layer on the second gate electrode and overlapping the second gate electrode, and a second source electrode and a second drain electrode on the second semiconductor layer. The first semiconductor layer and the second semiconductor layer are at a same layer of the display device, and each includes crystalline silicon germanium.