Devices and methods are provided for constructing a semiconductor structure that implements a PUF (physical unclonable function) based on a FinFET structure. The PUF is based on a random pattern of merged and non-merged source and drain structures, which are formed on adjacent semiconductor fin structures of adjacent pairs of FinFET devices, as a result of process-induced variations in the epitaxial growth of source and drain structures on the semiconductor fin structures. The random pattern of merged and non-merged source and drain structures provides a random pattern of electrical open and short connections between pairs of semiconductor fin structures, wherein the random pattern of electrical open and short connections defines the physical unclonable function.