US Patent 8115206 Semiconductor device

It is an object to provide a transistor having a new multigate structure in which operating characteristics and reliability are improved. In a transistor having a multigate structure, which includes two gate electrodes electrically connected to each other and a semiconductor layer including two channel regions connected in series formed between a source region and a drain region, and a high concentration impurity region is formed between the two channel regions; the channel length of the channel region adjacent to the source region is longer than the channel length of the channel region adjacent to the drain region.