A semiconductor device structure for a vertical field effect transistor comprises a substrate with a shallow trench isolation (STI) region. A lower source/drain area is formed on the STI region with a first semiconductor fin, a second semiconductor fin, and a third semiconductor fin. The third semiconductor fin is formed to couple the first semiconductor fin to the second semiconductor fin across the lower source/drain area. The STI region that is beneath the lower source/drain area comprises opposing sidewall portions curved in opposing directions. In one example the lower source/drain area is formed only at an intersection between the STI region and one or more of the first semiconductor fin, the second semiconductor fin, and the third semiconductor fin. In other example, the second semiconductor fin is disposed parallel to the first semiconductor fin and together with the third semiconductor fin resulting in an H-shaped structure from a top-down view.