TSMC reclaimed the 48,000-point level for Taiwan's Weighted Index on September 29, reversing from early losses after a 179-point intraday drop tied to the Mid-Autumn Festival catch-up selloff. The index opened with a 150.71-point gap down at 47,873.89 and touched 47,845.40 before recovering. By midmorning, it hovered near the flat line at the 48,000 threshold.

What drove the holiday-morning selloff?

Three major U.S. indices closed lower on Friday, and the Philadelphia Semiconductor Index led the declines. It fell 203.69 points, or 1.61%, to close at 12,465.24. Persistent U.S. Treasury yield gains and renewed Middle East tension after President Donald Trump rejected Iran's proposal to reopen the Strait of Hormuz drove the selling. Rising oil prices added pressure and weighed on risk appetite across global markets.

Friday's institutional flow data explains the concentrated selling at the open. On September 24, the last trading day before the holiday, three major institutional categories posted combined net selling of NT$44.449 billion, roughly $1.4 billion. Foreign investors sold a net NT$32.965 billion. Investment trusts sold a net NT$12.823 billion. Proprietary traders were the sole net buyers at NT$1.338 billion.

How did semiconductor stocks split the morning?

TSMC opened flat at NT$2,475 and climbed as much as NT$15 to NT$2,490, a 0.6% gain. Its New York ADR closed 0.5% higher on Friday, and Nvidia gained 1.68% in countertrend U.S. trading. The two signals together suggest institutional demand for AI leaders held firm despite the broader risk-off tone across technology names.

MediaTek carried the heaviest drag. It opened down NT$135 at NT$5,150 and fell to NT$5,130 intraday, a loss approaching 3%. Hon Hai opened down NT$3.5 at NT$247 before reversing higher to NT$252, up 0.6%. Delta Electronics opened down NT$30 at NT$1,880, then climbed to NT$1,915, a 0.26% gain. ASE Technology opened down NT$14 at NT$685 and traded near NT$690, down roughly 1.29%.

Where did the capital rotate?

General Interface Solution Holding surged to the daily limit at NT$89.4 on news of its expansion into high-end optical communications. Panel and solar names rose alongside it, pointing to active rotation into thematic small- and mid-cap stocks beyond the large-cap electronics complex.

Analyst Lin Han-wei framed the rotation in plain terms. He said: "With U.S. Treasury yields hitting a new swing high, investors have turned cautious on chasing large-cap electronics stocks, and whether small- and mid-cap names can attract renewed institutional inflows will be a key focus for the market going forward."

What changes the picture from here?

The U.S. Treasury yield trajectory, the Middle East situation, and foreign investor flows into Taiwan equities are the three variables traders cited. Morning trading volume had already cleared NT$100 billion, matching recent activity levels. Market participants indicated that if the index holds above 48,000, it may enter range-bound consolidation in the near term.

The mechanics are straightforward. Pre-holiday positioning left foreign investors and investment trusts heavily net short, so the open required forced selling. TSMC's reversal and the AI-related countertrend in U.S. trading absorbed the pressure and kept the 48,000 line intact. The next move likely depends on U.S. yields and energy prices, not on Taiwan-specific catalysts.

By Tom Whitfield