In a high frequency LDMOS transistor, a gate structure is formed on a substrate. A drain, doped with first type impurities at a first concentration, is formed on the substrate spaced apart from the gate structure. A buffer well, doped with the first type impurities at a second concentration lower than the first concentration, surrounds side and lower portions of the drain. A lightly doped drain, doped with the first type impurities at a third concentration lower than the second concentration, is formed between the buffer well and the gate structure. A source, doped with the first type impurities at the first concentration, is formed on the substrate adjacent to the gate structure and opposite to the drain with respect to the gate structure. Accordingly, an on-resistance decreases while a breakdown voltage increases in the LDMOS transistor without increasing a capacitance between the gate structure and the drain.