Structures for a cascode integrated circuit and methods of forming such structures. A field-effect transistor of the structure includes a gate electrode finger, a first source/drain region, and a second source/drain region. A bipolar junction transistor of the structure includes a first terminal, a base layer with an intrinsic base portion arranged on the first terminal, and a second terminal that includes one or more fingers arranged on the intrinsic base portion of the base layer. The intrinsic base portion of the base layer is arranged in a vertical direction between the first terminal and the second terminal. The first source/drain region is coupled with the first terminal, and the first source/drain region at least partially surrounds the bipolar junction transistor.