A Single-Event Upset (SEU) or Single-Bit Upset (SBU), is a radiation-induced failure, where one or more values stored in memory are corrupted.

They usually occur in RAM or Flash memory cells where a capacitor is used to store the state of the cell. A high energy particle hitting either the capacitor, the transistors that control the state of the capacitor, or even the electronics that sense the state of the bit during read operations.

Single-event upsets can be detected with error-correcting codes or error-detection and correction schemes.

An error that affect multiple bits is a multiple-bit upset.