Counterfeit electronics entering the globalized supply chain are a growing problem impacting manufacturers and consumers alike. This article introduces Flash-DNA, a new technique for identifying the original chip manufacturer of NAND flash memory, which will help preventing the proliferation of rebranded or cloned flash memory chips. Flash-DNA relies on extracting intrinsic variations in NAND arrays using a partial block erase operation. Our experimental evaluation, conducted on multiple memory chips from four major manufacturers, shows that Flash-DNA captures fundamental properties of the manufacturing process, providing a unique identifier for a family of NAND flash memory chips that can be used for tracing their origins.