Embodiments of three-dimensional (3D) ferroelectric memory devices and methods for forming the ferroelectric memory devices are disclosed. In an example, a 3D ferroelectric memory device includes a substrate and a plurality of ferroelectric memory cells each extending vertically above the substrate. Each of the ferroelectric memory cells includes a capacitor and a transistor electrically connected to the capacitor. The capacitor includes a first electrode, a second electrode, and a ferroelectric layer disposed laterally between the first electrode and the second electrode. The transistor includes a channel structure, a gate conductor, and a gate dielectric layer disposed laterally between the channel structure and the gate conductor.