A vertical channel transistor structure is provided. The structure includes a substrate, a channel, a cap layer, a charge trapping layer, a source and a drain. The channel is formed in a fin-shaped structure protruding from the substrate. The cap layer is deposited on the fin-shaped structure. The cap layer and the fin-shaped structure have substantially the same width. The charge trapping layer is deposited on the cap layer and on two vertical surfaces of the fin-shaped structure. The gate is deposited on the charge trapping layer and on two vertical surfaces of the fin-shaped structure. The source and the drain are respectively positioned on two sides of the fin-shaped structure and opposite the gate.