Physically unclonable function (puf) generation involving high side programming of bits

A method of operating a semiconductor device comprising resistive switching devices, comprising:

• enabling an identifier acquisition sequence for a semiconductor chip;
• identifying a set of never-programmed resistive switching devices on the semiconductor chip for the identifier acquisition process;
• applying a voltage below a program voltage to a set of never-programmed resistive switching devices of an array of resistive switching memory devices of the circuit;
• reading an associated native current for each resistive switching device of the set of never-programmed resistive switching devices relative to a first threshold current value;
• determining a first group of switching devices having a first digital value in response to having associated native currents above the first threshold current value, and a second group of switching devices having a second digital value in response to having associated native currents below the first threshold current value, wherein the first digital value is different from the second digital value;
• mapping the digital values determined for the set to an additional identifier bit sequence;
• and
• applying a program voltage to one of the first group of switching devices or the second group of switching devices to cause either the first group of switching devices or the second group of switching devices to become programmed non-volatile resistive switching devices.