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　approximate　to　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　216384/mu　m2.　For　practical　applications,　detection　of　fingerprints　protected　with　a　polymer　coating　is　demonstrated　using　back-scattered　electron　imaging.