A fourth straight gain, and a new leader
The TAIEX closed Monday at 47,718.84, up 1.14% — a three-month high and a fourth consecutive winning session. The lead-in helped: the Philadelphia Semiconductor Index rose 2.78% in Friday’s US session while the S&P 500 added a modest 0.17%, and S&P 500 futures firmed a further 1.24% to 7,752 during Asian hours, giving the tape a supportive backdrop from open to close.
But the defining story was MediaTek, which surged 6.37% to NT$5,010 after unveiling its Dimensity 9600 Pro mobile chipset — built on TSMC’s 2nm process and pitched at on-device agentic AI — alongside forecasts that its data-center AI chip revenue will exceed US$2 billion in 2026. NVIDIA and international institutions backing the company’s US$3.9 billion convertible bond issuance added a stamp of large-scale institutional appetite. TSMC, which carries over 40% of the market’s capitalization, rose 0.81% to NT$2,480 as its 3nm, 4nm and 5nm lines remain fully booked against AI accelerator demand, with attention turning to potential foundry price increases slated for 2027.
By sector, semiconductors gained 1.21%, financials and insurance 0.82%, and shipping lagged at 0.25%. Hon Hai was the notable laggard among heavyweights, slipping 0.20% to NT$250. UMC added 0.64% to NT$157. The Taiwan dollar firmed, with USD/TWD easing 0.28% to 31.76 at Monday’s close.
Institutional flows: all three groups on the buy side
Monday’s official TWSE data showed unanimous institutional buying — the broadest configuration and the one that matters most for follow-through:
| Investor group | Net trading value (2026-09-21) |
|---|---|
| Foreign investors | NT$+20.38B (net buy) |
| Investment trusts | NT$+3.93B (net buy) |
| Dealers (proprietary + hedge) | NT$+22.73B (net buy) |
| Combined | NT$+47.04B |
Foreign investors bought NT$20.38 billion net in the cash market, investment trusts added NT$3.93 billion, and dealers were the largest single buyer at NT$22.73 billion. A combined NT$47.04 billion of institutional buying on a day the index broke to a three-month high is a clean alignment of price and flow. It squares with the domestic mood: Cathay Financial’s monthly survey, released Monday, showed a notable rebound in public economic optimism and equity risk appetite, underpinned by AI earnings visibility.
Positioning: what Friday’s leverage and short data showed
Monday’s margin and securities-lending figures publish after the fact, so the latest available positioning data is from Friday’s session (September 18). Keeping the three channels distinct, as always:
- Retail leveraged longs (margin purchases): the market-wide margin loan balance stood at NT$594.0 billion as of Friday, up NT$4.64 billion on the session — retail leverage building modestly into the advance. At the stock level, Hon Hai margin balances rose 1,615 lots while TSMC (-385 lots) and especially UMC (-20,799 lots) saw retail longs trimmed.
- Institutional shorts (SBL balances): breadth leaned toward more shorting — balances rose in 632 shortable issues versus falling in 273 on Friday. But the pressure was not on Monday’s leaders: MediaTek’s SBL balance fell 107,594 shares and TSMC’s fell 66,000 heading into the session, while Hon Hai’s rose 1,058,400 shares — consistent with its underperformance Monday, with retail longs and institutional shorts both leaning into the same name from opposite sides.
The overall read: rising retail leverage plus broadening institutional short balances against unanimous cash-market buying makes for a market that is trending but no longer under-owned. That is context, not a signal — Monday’s own positioning prints arrive Tuesday.
Valuations and the ADR gap
Monday’s rally came with the leadership trading rich. As of Friday’s close, MediaTek carried a PER of 77.79 and PBR of 17.72; TSMC a PER of 28.52 and PBR of 9.92; Hon Hai remains the value anchor among the heavyweights at a PER of 16.51 and a 2.86% yield. Foreign ownership is heaviest in TSMC at 69.22% of shares outstanding, with Delta Electronics at 61.59% and MediaTek at 56.22%.
On TSMC’s ADR: the New York close of US$434.67 on Friday stood 11.3% above Monday’s Taipei close on a five-shares-per-ADR basis. Two caveats apply, as ever. The premium is structural — it has run roughly 15-25% in recent years owing to limited fungibility — and the two closes are from different sessions, so the level itself signals nothing. What is worth noting is that the measured gap sits below that recent structural range; whether Monday night’s US session restores it, or the compression persists, is the actual information.
What to watch
- Tuesday’s positioning prints: whether Monday’s 6.37% MediaTek move pulled retail margin longs into the name, and whether the market-wide margin balance extends its climb past NT$594.0 billion.
- Foreign flow persistence: NT$20.38 billion of foreign buying confirmed the breakout; a second consecutive session of net buying would suggest the three-month high is being accumulated into rather than sold.
- The US handoff: S&P futures were up 1.24% at 7,752 during Taiwan hours — whether the cash session validates that, and what it does to the TSMC ADR gap, sets Tuesday’s open.
Disclaimer: This is an information and analysis publication, not investment advice. See our Methodology for data sources, standards, and our corrections policy.