FinFET varactors having low threshold voltages and methods of making the same are disclosed herein. An exemplary FinFET varactor includes a fin and a gate structure disposed over a portion of the fin, such that the gate structure is disposed between a first source/drain feature and a second source/drain feature that include a first type dopant. The portion of the fin includes the first type dopant and a second type dopant. A dopant concentration of the first type dopant and a dopant concentration of the second type dopant vary from an interface between the fin and the gate structure to a first depth in the fin. The dopant concentration of the first type dopant is greater than the dopant concentration of the second type dopant from a second depth to a third depth in the fin, where the second depth and the third depth are less than the first depth.