A method (100) is disclosed of generating an identifier from a semiconductor device (600) comprising a volatile memory (610) having a plurality of memory cells. The method comprises causing (110) the memory cells to assume a plurality of pseudo-random bit values inherent to variations in the microstructure of the memory cells; retrieving (120) the bit values from at least a subset of the plurality of memory cells; and generating the identifier from the retrieved bit values. The method (100) is based on the realization that a substantial amount of the cells of a volatile memory can assume a bit value that is governed by underlying variations in manufacturing process parameters; this for instance occurs at power-up for an SRAM or after a time period without refresh for a DRAM. This can be used for several identification purposes, such as identifying a semiconductor device (600) comprising the volatile memory (610), or for secure key generation by mapping error-correcting code words onto the identifier bit locations. The present invention further includes a semiconductor device (600, 1000) configured to be subjectable to the method (100) of the present invention.