In secure communication, users must have a method of authenticating the identity of the recipients of their data, and vice versa. This requires the capability of generating a unique yet reproducible signature under a variety of environmental conditions. At present, these unique signatures are widely generated by Physically Unclonable Functions, or PUFs, which use physical characteristics of specific structures containing inherent randomness due to their manufacturing process. These hard to predict physical responses are quantised to generate a unique identity which can be used for authentication. However, these devices are size-limited by their classical design, posing challenges to microelectronic implementation. Here we show that the extensively studied and problematic fluctuations in the current-voltage measurements of Resonant Tunnelling Diodes (RTDs) can be reapplied to function as a PUF without conventional size limitations. This is possible due to quantum-mechanical tunnelling within the RTD, and, on account of these room temperature quantum effects, we term such devices QUFs – Quantum Unclonable Functions. When stimulated with a range of voltages, these devices produce a range of current outputs whilst exhibiting characteristic negative differential resistance in the region where resonant tunnelling takes place. The resultant current-voltage spectra are dependent on the exact atomic structure and composition of the quantum well within the RTD, and so are unique to the device in question. This allows us to create ‘PUF-like’ devices at the on-chip scale which explicitly make use of room-temperature quantum phenomena and subsequently provides a path towards resource-low quantum authentication protocols.