Methods of forming backside vias connected to source/drain regions of long-channel semiconductor devices and short-channel semiconductor devices and semiconductor devices formed by the same are disclosed. In an embodiment, a semiconductor device includes a first transistor structure; a second transistor structure adjacent the first transistor structure; a first interconnect structure on a front-side of the first transistor structure and the second transistor structure; and a second interconnect structure on a backside of the first transistor structure and the second transistor structure, the second interconnect structure including a first dielectric layer on the backside of the first transistor structure; a second dielectric layer on the backside of the second transistor structure; a first contact extending through the first dielectric layer and electrically coupled to a first source/drain region of the first transistor structure; and a second contact extending through the second dielectric layer and electrically coupled to a second source/drain region of the second transistor structure, the second contact having a second length less than a first length of the first contact.