1. A transistor comprising: a channel layer, the channel layer including a plurality of unit layers spaced apart from each other in a vertical direction, and each of the plurality of unit layers including a plurality of unit channels spaced apart from each other in a horizontal direction, each of the plurality of unit channels including a plurality of nanostructures, the plurality of nanostructures in each of the plurality of unit channels including a network structure, the plurality of unit channels in each of the plurality of unit layers forming a stripe pattern; a source arranged laterally on one side of the channel layer; a drain arranged laterally on an other side of the channel layer; and a gate corresponding to the channel layer; and an insulation layer between every two adjacent unit layers, the insulation layer including a first insulation single layer between first and second unit layers of the plurality of unit layers, the first and second unit layers directly contacting lower and upper surfaces of the first insulation single layer, respectively.