A method of forming a semiconductor device may include forming a fin structure extending from a substrate. The fin structure may include first and second source/drain regions and a channel region therebetween, and the first and second source/drain regions may extend a greater distance from the substrate than the channel region. A gate insulating layer may be formed on the channel region, and a gate electrode may be formed on the gate insulating layer so that the gate insulating layer is between the gate electrode and the channel region. Related devices are also discussed.