Taiwan’s first session back from the Mid-Autumn Festival holiday was a catch-up trade, and the direction was down. The TAIEX fell 392.64 points, or 0.82%, to close Tuesday at 47,631.96, after opening at 47,873.89 and touching an intraday low of 47,573.09. Turnover was heavy at NT$785.04 billion. The proximate cause sat offshore: while Taipei was closed, all four major US indices sold off — the S&P 500 lost 0.77% and the Philadelphia Semiconductor Index 1.61% in Monday’s US session — on surging Treasury yields, stalled US–Iran negotiations, and climbing crude prices. Taipei priced all of that in one sitting.
Institutional flows: foreigners sell in size
The flow picture, this site’s daily signature, was unambiguous. Foreign institutional investors were heavy net sellers, and proprietary dealers joined them; only the domestic investment trusts leaned the other way, and modestly.
| Investor type (TWSE, Sept 29) | Net trading value |
|---|---|
| Foreign investors | −NT$63.20B (net sell) |
| Investment trusts | +NT$1.42B (net buy) |
| Dealers (proprietary + hedge) | −NT$16.40B (net sell) |
| Three institutions combined | −NT$78.19B |
A combined NT$78.19 billion outflow is a serious number for a single session, and it showed up in the currency as well (more below). In the futures market, the most recent published TAIFEX data — from Thursday, September 24, the last session before the holiday; today’s figures are not yet out — had foreign investors’ TAIEX futures net open interest at −77,031 contracts, with a small −909 contracts of net volume that day. That is pre-holiday positioning, not a read on today’s action, but it means foreigners came into this week already carrying a sizable short book in index futures, and today’s cash selling landed on top of it.
Semis: MediaTek takes the hit, TSMC absorbs it
The day’s single-stock story was MediaTek (2454), which fell NT$375, or 7.10%, to NT$4,910 — surrendering the NT$5,000 psychological level — following market reports of adjusted order allocations from Google. The stock came into the session richly priced: at the September 24 TWSE reading, MediaTek carried a trailing PER of 87.28 and a PBR of 19.89, leaving little cushion for order-book disappointment.
TSMC (2330), by contrast, did the index a favor. It traded as high as NT$2,495 in the morning before fading to close exactly flat at NT$2,475. Hon Hai (2317) was likewise unchanged at NT$250.50, and UMC (2303) slipped just 0.32% to NT$153.50. That resilience in the heavyweights explains an apparent oddity in the tape: the TWSE Semiconductor sub-index actually rose 0.88% even as the broad index fell — TSMC’s flat close and strength elsewhere in the sector outweighed MediaTek’s slide, while the index-level damage came from the AI hardware complex, where high-multiple server, thermal-cooling, and PCB/ABF substrate names saw profit-taking. Quanta (2382) eased NT$2 to NT$336.5.
On the ADR cross-check: TSM closed Monday’s US session at $452.88, which works out to roughly a 16.7% premium over Tuesday’s Taipei close. Two caveats, as always. The premium is structural — it has run roughly 15–25% in recent years given limited fungibility — and the two closes come from different sessions. At 16.7% the gap sits toward the lower end of its recent band; the level itself is not a mispricing signal, and only day-to-day changes in the gap carry information.
Rotation: oil beneficiaries and shipping catch a bid
Not everything went down. Rising crude prices — a headwind for tech multiples — were a direct tailwind for the petrochemical complex. Formosa Petrochemical (6505) jumped more than 8%, reclaiming its annual moving average, with Formosa Plastics, Nan Ya Plastics, and Formosa Chemicals advancing alongside it. The Shipping sub-index gained 2.08% and Financials & Insurance added 0.54%, giving the session a distinct old-economy-rotation flavor. A handful of mid- and small-cap tech names went the other way entirely, hitting the 10% daily limit up: GIS-KY (6456), Andes Technology (6533), and Po-Teng Technology (3518).
Currency: TWD under pressure
The Taiwan dollar weakened alongside the equity outflows, with USD/TWD quoted around 31.9 during Tuesday trading. The pair opened at 31.800 and spent the session grinding higher on foreign-capital repatriation, with exporter selling reported as the main source of resistance on the way up. Continued cash-market selling of this magnitude, if it persists, keeps the depreciation pressure alive.
The setup from here
Overnight risk sentiment offers a mildly steadier footing: S&P 500 futures were little changed during Taiwan hours, off 0.07% at 7,741.25 — not a recovery signal, but not an extension of Monday’s US selloff either. The question for Wednesday is whether today’s NT$63.2 billion foreign sale was a one-off holiday catch-up or the start of a sustained distribution, particularly with the futures short base already elevated coming into the week.
What to watch
- Tonight’s TAIFEX release: the first post-holiday update to foreign investors’ TX net open interest (last published at −77,031 contracts on Sept 24) — whether today’s cash selling was hedged, extended, or covered in futures.
- MediaTek follow-through: whether the Google order-allocation story draws clarification, and whether NT$4,910 holds after the loss of the NT$5,000 level on an 87x trailing multiple.
- USD/TWD around 31.9: a second straight session of heavy foreign outflows would test how far exporter selling can lean against the move.
Disclaimer: This is an information and analysis publication, not investment advice. See our Methodology for data sources, standards, and our corrections policy.