A method for forming a semiconductor device, the method comprising: forming a first dummy gate part extending across a first fin and a second dummy gate part extending across a second fin , said first dummy gate part extending in a first gate trench section in an insulating layer and said second dummy gate part extending in a second gate trench section in the insulating layer , removing said first dummy gate part selectively to said second dummy gate part , wherein each of the first and second fins is formed by a layer stack comprising a first layer and a second layer on the first layer, the first layer comprising Si 1-x Ge x and the second layer comprising Si 1-y Ge y , wherein 0≤ x≤1 and 0≤y≤1 and x≠y, forming a silicon capping layer on the portion of the first fin exposed in said first gate trench section , performing an oxidation process to oxidize the silicon capping layer and to oxidize an outer thickness portion of said portion of the first fin such that a trimmed fin portion comprising laterally trimmed portions of said first and second layers remains inside the oxidized outer thickness portion , subsequent to performing the oxidation process, removing the second dummy gate part while the oxidized silicon capping layer and the oxidized outer thickness portion covers said trimmed fin portion , removing the oxidized silicon capping layer and the oxidized outer thickness portion from said trimmed fin portion , removing the laterally trimmed portion of the first layer exposed in the first gate trench section and the portion of the first layer exposed in the second gate trench section , and forming a final gate structure around the laterally trimmed second layer portion in the first gate trench section and around the second layer portion in the second gate trench section . forming a first dummy gate part extending across a first fin and a second dummy gate part extending across a second fin , said first dummy gate part extending in a first gate trench section in an insulating layer and said second dummy gate part extending in a second gate trench section in the insulating layer , removing said first dummy gate part selectively to said second dummy gate part , wherein each of the first and second fins is formed by a layer stack comprising a first layer and a second layer on the first layer, the first layer comprising Si 1-x Ge x and the second layer comprising Si 1-y Ge y , wherein 0≤ x≤1 and 0≤y≤1 and x≠y, forming a silicon capping layer on the portion of the first fin exposed in said first gate trench section , performing an oxidation process to oxidize the silicon capping layer and to oxidize an outer thickness portion of said portion of the first fin such that a trimmed fin portion comprising laterally trimmed portions of said first and second layers remains inside the oxidized outer thickness portion , subsequent to performing the oxidation process, removing the second dummy gate part while the oxidized silicon capping layer and the oxidized outer thickness portion covers said trimmed fin portion , removing the oxidized silicon capping layer and the oxidized outer thickness portion from said trimmed fin portion , removing the laterally trimmed portion of the first layer exposed in the first gate trench section and the portion of the first layer exposed in the second gate trench section , and forming a final gate structure around the laterally trimmed second layer portion in the first gate trench section and around the second layer portion in the second gate trench section . <EOS>