Taiwan’s benchmark TAIEX fell 667.25 points, or 1.42%, to close Thursday at 46,368.33, recovering only part of an intraday plunge of more than 980 points that took the index below its quarterly and short-term moving averages. Turnover was heavy at NT$789.2 billion. The selling had three distinct drivers: a sharp post-earnings reaction in United Microelectronics Corp., a bruising session for AI-adjacent electronics after mixed US big-tech results, and the return of foreign institutions as aggressive net sellers.
Semiconductors: UMC limit-down, MediaTek slides, TSMC holds up
UMC (2303) was the day’s defining single-stock story, plunging 9.77% to its limit-down price of NT$115.50 on the market’s highest trading volume. The trigger was a quarterly net profit decline of over 6%, flattered-base effects from non-operating items in the prior quarter overshadowing what was otherwise a constructive report: record third-quarter wafer shipments, core operating profit growth, an additional US$3.2 billion capital expenditure plan for silicon photonics and advanced packaging, and guidance for roughly 10% year-over-year growth in 2027 average selling prices. At Tuesday’s TWSE valuation snapshot, UMC traded at 19.25x earnings and 3.62x book — the market evidently had little tolerance for a headline earnings miss at that multiple.
- MediaTek (2454) fell 4.49% to NT$4,045, the heaviest drag among large-cap IC designers.
- TSMC (2330) showed relative resilience, slipping just 0.41% to NT$2,415. Its US-listed ADRs closed Wednesday at $439.51, roughly 18% above the Taipei close — comfortably within the structural 15–25% premium the ADRs have carried in recent years, and comparing closes from different sessions, so nothing to read into the level itself.
- Hon Hai (2317) lost 1.39% to NT$248.
- Delta Electronics (2308) dropped NT$70, or 4.52%, to NT$1,480 after inventory write-down losses at its Thai subsidiary weighed on near-term margin expectations ahead of its investor conference.
Selling was concentrated in electronics, glass and optoelectronics, with defensive rotation visible into financials: the Financials & Insurance sub-index rose 1.05% and Shipping added 0.78% against the falling tape.
Institutional flows: foreigners sell NT$68.8 billion, trusts keep buying
The three major institutional categories combined for a net sell of NT$81.67 billion on Thursday, ending their prior buying streak.
| Investor type | Net flow (NT$, Oct 29) | Direction |
|---|---|---|
| Foreign investors | -68.82 billion | Net sell |
| Investment trusts | +8.65 billion | Net buy (13th straight session) |
| Dealers (prop + hedge) | -21.50 billion | Net sell |
| Combined | -81.67 billion | Net sell |
Foreign institutions, rebalancing and locking in gains, did the bulk of the damage. Dealer selling was overwhelmingly hedging-related (NT$21.3 billion of the NT$21.5 billion total) rather than directional proprietary positioning. The standout on the other side remains the domestic investment trusts, which extended their buying streak to thirteen consecutive sessions — a domestic bid that leaned against Thursday’s foreign outflow.
Positioning and leverage: where the books stood going in
Derivatives and leverage data are published with a one-day lag, so the following describes Wednesday’s (Oct 28) close — the setup before today’s slide, not a reaction to it. Foreign investors carried a net short of 84,917 contracts in TAIEX futures into the session, after a marginal net buy of 1,050 contracts on the day. The options put/call volume ratio stood at 92.29%, not an extreme reading in either direction.
On the leverage side, the market-wide margin loan balance — retail leveraged longs — rose NT$8.91 billion to NT$632.3 billion as of Wednesday. Notably, retail traders added to leveraged long positions in UMC (margin balance up 1,017 lots to 150,043) heading into the earnings print that produced today’s limit-down. In the institutional short channel, SBL balances told a mixed story as of Wednesday: UMC’s lending balance actually fell by 8.24 million shares, Hon Hai’s rose by about 1.08 million shares, and TSMC’s rose by 535,000 shares. Breadth across shortable issues was essentially balanced — balances up in 446 names, down in 438 — so the pre-session positioning picture was one of an established foreign futures short and growing retail long leverage, rather than any broad institutional short build-up.
Currency and the global backdrop
The equity outflow bled directly into the currency. The Taiwan dollar opened firmer at NT$32.390 per US dollar before reversing to an intraday low of NT$32.564, with USD/TWD finishing at 32.54, up 0.37% — a simultaneous stock-and-currency sell-off that is the classic signature of foreign repatriation days.
The irony is that the overnight US lead was positive: the Philadelphia Semiconductor Index rose 1.75% and the S&P 500 added 0.28% on Wednesday. But a sharp after-hours drop in Alphabet shares on cash flow and earnings concerns reframed the session, intensifying scrutiny of how quickly massive AI capital expenditure converts into revenue — a question that lands squarely on Taiwan’s AI supply chain. S&P 500 futures traded down 0.32% during Taiwan hours, reinforcing the cautious tone into the close.
What to watch
- Thursday’s TAIFEX data (published Friday): whether foreign investors deepened their 84,917-contract futures net short in tandem with the NT$68.8 billion cash-market sale, or used the dip to cover.
- USD/TWD around the 32.5 handle: a further push above Thursday’s 32.564 intraday low would signal continued foreign repatriation pressure.
- Delta Electronics’ investor conference and the trusts’ streak: whether management quantifies the Thai write-down damage, and whether investment trusts stretch their buying run to a fourteenth session against the foreign tide.
Disclaimer: This is an information and analysis publication, not investment advice. See our Methodology for data sources, standards, and our corrections policy.