The increasing vulnerability of microchips to counterfeiting poses a significant threat to nations, companies, and the general public. Creating a unique "fingerprint" on each chip using intrinsic manufacturing variations can significantly prevent the number of fraudulent chips. Since Si-based semiconductor fabrication processes are now flawless down to a few nanometers, finding a high-entropy source at the nanoscale has become challenging. Inspired by the concept of physical unclonable function, this work reports the CMOS-compatible and lithography-free fabrication of unique nanostructured silicon "fingerprints." Nanostructuring is achieved via low-temperature dewetting and metal-assisted chemical etching, which produces a high level of entropy and unique silicon-based nanoscale fingerprints with linewidths tunable from ≈8 to 140 nm, commensurate with the dimensions of mainstream microfabrication processes. These Si nanofingerprints are highly reliable for chip authentication and against reverse engineering, providing a large encoding capacity of up to 2