Provided are metal oxide field-effect transistor (MOSFET) devices having a metal gate structure, in which a work function of the metal gate structure is uniform along a length direction of a channel, and manufacturing methods thereof. The MOSFET devices include a semiconductor substrate, an active area on the semiconductor substrate and extending in a first direction, and a gate structure on the semiconductor substrate. The gate structure extends across the active area in a second direction that traverses the first direction and comprises a high-k layer, a first metal layer, a work function control (WFC) layer, and a second metal layer, which are sequentially stacked on the active area. A lower surface of the WFC layer may be longer than a first interface between a lower surface of the first metal layer and an upper surface of the high-k layer in the first direction.