Devices and methods for forming a device are disclosed. A substrate is provided. A plurality of fin structures are formed in the substrate. The fin structures include an upper part and a lower part. An isolation layer is formed on the substrate. The lower part of the plurality of fin structures is embedded in the isolation layer. A source including a first source portion and a second source portion is formed in a first side of the substrate. The first source portion partially occupies the fin structures along a length direction. The second source portion is formed over the first source portion. The second source portion elevates the fin structures. A drain is formed in a second side of the substrate. A distance between the source to the drain defines a channel region. A gate having a gate dielectric and a metal gate electrode is formed over the substrate. The gate wraps around the elevated fin structures and channel region.