A semiconductor device includes a semiconductor substrate, a trench formed in the semiconductor substrate, an island-like element region formed in the semiconductor substrate, having an upper surface, first to third side surfaces, an upper portion, a middle portion and a lower portion, a gate insulating film formed on the first to third side surfaces in the upper portion of the element region, a gate electrode having first and second bottom surfaces, a first diffusion layer formed along the upper surface of the element region, a second diffusion layer formed along the first side surface in the middle portion of the element region, a channel region having first to third regions formed along the first to third side surfaces in the upper portion of the element region, a capacitor formed in the trench, and a bit line electrically connected to the first diffusion layer.