United Microelectronics (UMC) shares plummeted 5.76% in the pre-market session, as a broad sell-off across the global semiconductor sector intensified. The steep decline reflects contagion from a systemic risk-off event that has swept through the chip supply chain.

The sell-off was triggered by escalating concerns over an artificial intelligence bubble, with fears that AI-related demand may have been artificially inflated. This sentiment was amplified after South Korea's KOSPI index plunged as much as 9.6%, triggering a temporary trading halt, and major chipmakers Samsung Electronics and SK Hynix each dropped over 11%. Meanwhile, reports of NVIDIA's transactions exceeding $750 billion further fueled market anxiety about the sustainability of AI-driven growth.

Adding to the pressure, United Microelectronics is scheduled to release its second-quarter earnings report later today. Market consensus projects quarterly revenue of $2.044 billion, a 9.28% year-over-year increase, with adjusted earnings per share of $0.15. Investors remain cautious about the company's capacity utilization guidance, mature-node pricing trends, and updates on its 12nm collaboration with Intel.