A method of forming an integrated circuit includes forming at least one transistor over a substrate. The at least one transistor includes a first gate dielectric structure disposed over a substrate. A work-function metallic layer is disposed over the first gate dielectric structure. A conductive layer is disposed over the work-function metallic layer. A source/drain (S/D) region is disposed adjacent to each sidewall of the first gate dielectric structure. At least one resistor structure is formed over the substrate. The at least one resistor structure includes a first doped semiconductor layer disposed over the substrate. The at least one resistor structure does not include any work-function metallic layer between the first doped semiconductor layer and the substrate.