According to some embodiments of the invention, transistors have channel regions between channel-portion holes. Methods of forming the same include at least two channel-portion holes disposed in a semiconductor substrate. Line patterns are formed in parallel to be spaced apart from each other on a main surface of the semiconductor substrate to fill the channel-portion holes. A channel region is disposed in the semiconductor substrate below the line patterns. At this time, the channel region is formed between the channel-portion holes and also covers lower portions of the channel-portion holes. Driving current capability and refresh characteristics of DRAMs utilizing the inventive transistors are improved.