An integrated circuit for a physically unclonable function (PUF) includes first and second PUF cells and a combination circuit. The first and second PUF cells respectively output first and second cell signals having unique levels based on a threshold level of a logic gate. The combination circuit includes a first stage that generates a first combination signal based on the first and second cell signals. The first and second PUF cells respectively include first and second logic gates to respectively output the first and second cell signals. The combination circuit includes a third logic gate that receives the first and second cell signals and outputs the first combination signal. The third logic gate has a same structure as each of the first and second logic gates.