Semiconductor device structure and method for forming the same

A semiconductor device structure, comprising:

• a substrate;
• a first fin structure and a second fin structure disposed over the substrate;
• a first gate stack disposed over the substrate and overlapping the first fin structure, wherein the first gate stack has a first width, the first gate stack comprises a first work function layer, and a first top surface of the first work function layer is positioned above the first fin structure by a first distance;
• and
• a second gate stack disposed over the substrate and overlapping the second fin structure, wherein the first width is less than a second width of the second gate stack, the second gate stack comprises a second work function layer, the first work function layer and the second work function layer are made of a same material, a second top surface of the second work function layer is positioned above the second fin structure by a second distance, and the first distance is less than the second distance,
• wherein the first gate stack further comprises a third work function layer over the first work function layer, the third work function layer covers the first top surface, and the third work function layer includes a p-type or n-type metal.