A
single event upset (
SEU) is a change of state caused by one single ionizing particle (ions, electrons, photons...) striking a sensitive node in a micro-electronic device, such as in a
microprocessor,
semiconductor memory, or power
transistors. The state change is a result of the free charge created by
ionization in or close to an important node of a logic element (e.g. memory "bit"). The error in device output or operation caused as a result of the strike is called an SEU or a
soft error.