Transistor device and method of forming the same

Transistor devices are provided. A transistor device includes a substrate. The transistor device includes a lower transistor having a lower gate and a lower channel region on the substrate. The transistor device includes an upper transistor having an upper gate and an upper channel region. The lower transistor is between the upper transistor and the substrate. The transistor device includes an isolation region that separates the lower channel region of the lower transistor from the upper channel region of the upper transistor. Moreover, the lower gate of the lower transistor contacts the upper gate of the upper transistor. Related methods of forming a transistor device are also provided.