Semiconductor devices and methods of forming the same are provided. A semiconductor device according to the present disclosure includes a ferroelectric structure including a channel region and a source/drain region, a gate dielectric layer disposed over the channel region of the ferroelectric structure, a gate electrode disposed on the gate dielectric layer, and a source/drain contact disposed on the source/drain region of the ferroelectric structure. The ferroelectric structure includes gallium nitride, indium nitride, or indium gallium nitride. The ferroelectric structure is doped with a dopant.