On June 26, UMC fell 6.13% in regular trading, trading at $25.28/share, with turnover of $59.61 million. The decline was driven by broad semiconductor sector weakness combined with concentrated profit-taking pressure following the stock's sharp recent rally.

On the news front, the semiconductor sector saw widespread selling, with Micron Technology down 5.89%, Marvell Technology down 5.5%, AMD down 4.24%, and Intel down 3.66%, dragging sector sentiment lower. UMC had previously surged on multiple catalysts including rumors of a partnership with Intel to co-develop 3nm and 12nm process technologies at Intel's Arizona fab, as well as expectations of customer order transfers following reports of TSMC cutting 28nm production by 25%. However, the company issued a statement on the Taiwan Stock Exchange stating it would not comment on speculative reports or market rumors, urging investors to rely solely on official disclosures. Market uncertainty over the partnership's confirmation intensified selling pressure as accumulated gains were unwound.

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