An electric physical unclonable function (PUF) (100) is provided comprising a semiconductor memory element (110) connectable to a PUF control means for reading content from the memory element and for deriving at least in part from said content a digital identifier, such as a secret key. Upon powering the memory element it settles into one of at least two different stable states. The particular stable state into which the memory element settles is dependent at least in part upon random physical characteristics of the memory element introduced during manufacture of the memory element. Settling of the memory element is further dependent upon a control input (112) of the memory element. The electric physical unclonable function comprises shielding means (142, 144) for shielding, during a time period including the power-up of the memory element and lasting at least until the settling of the memory element, the control input from receiving control signals upon which the particular stable state into which the memory element settles is dependent. In this way, the dependency of the memory element on its physical characteristics is improved, and dependency on possibly irreproducible control signals is reduced.