The ESD9X3.3ST5G is a transient voltage suppressor (TVS) made by ON Semiconductor with a SOD-923 package. It has two diodes for protection from electrostatic discharge events, which can damage and disrupt electronics and other components. The TVS is rated to protect up to 3.3V and has a power dissipation rating of 5W. The ESD9X3.3ST5G is designed for low capacitance and high breakdown voltage to ensure effective protection. It is often used in data lines, automotive systems, and other equipment with sensitive circuitry.