Integrated circuit semiconductor device and method of manufacturing the same

An integrated circuit semiconductor device includes a first region including a first transistor and a second region in contact with the first region in a second direction. The first transistor includes a first active fin extending in a first direction, a first gate dielectric layer extending from the first active fin onto a first isolation layer in the second direction, and a first gate electrode on the first gate dielectric layer. The second region includes a second transistor including a second active fin extending in the first direction, a second gate dielectric layer extending from the second active fin onto a second isolation layer in the second direction, and a second gate electrode on the second gate dielectric layer. The integrated circuit semiconductor device includes a gate dielectric layer removal region proximate a boundary between the first region and the second region.