A semiconductor device includes an insulating base including a trench, a transistor including a gate electrode and vertical channel in the trench, and a source electrode in the insulating base outside the trench, an isolation layer on the gate electrode in the trench, and a capacitor including a trench capacitor portion that is on the isolation layer in the trench, and a stacked capacitor portion that is coupled to the source electrode of the transistor outside the trench.