Semiconductor devices including a through via structure and methods of forming the same are provided. The semiconductor devices may include a semiconductor substrate including a first surface and a second surface opposite the first surface, a front insulating layer on the first surface of the semiconductor substrate, a back insulating layer on the second surface of the semiconductor substrate, a through via structure extending through the back insulating layer, the semiconductor substrate, and the front insulating layer, a via insulating layer on a side surface of the through via structure, and a contact structure extending through the front insulating layer. The through via structure may include a first region and a second region disposed on the first region. The second region may include a first doping element, and the first region may be substantially free of the first doping element.