TSMC carries roughly 35% or more of the TAIEX’s capitalization weight, so a 1% move in the stock mechanically shifts Taiwan’s benchmark by about 0.35 percentage points before any other share trades. Here is how to decompose any TAIEX session into its TSMC and non-TSMC components — with worked examples from real July 2026 data.
Taiwan’s benchmark fell 3.76% to 40,039.18 on Wednesday, its fourth straight decline, as skepticism over AI infrastructure returns hit semiconductors. Foreign investors sold NT$22.25B in cash equities while investment trusts bought against the tide.
Taiwan’s benchmark fell 4.65% to 41,603 on Tuesday as foreign investors dumped a net NT$87.56 billion. MediaTek and UMC fell close to 10%, TSMC lost 2.98%, and the sell-off tracked a region-wide unwind of AI infrastructure trades.
Taipei absorbed a -4.25% overnight drop in the Philadelphia Semiconductor Index with barely a scratch: the TAIEX closed at 43,634.19, down just 0.05%, as foreign investors net bought NT$8.04B and financials rallied 1.45%. MediaTek and UMC bore the brunt while TSMC ended unchanged.
The TAIEX surged 4.20% to 44,232.87 on Tuesday, clawing back part of Friday’s historic 6.47% rout. But the rebound was domestically funded: investment trusts bought NT$17.23B while foreign investors stayed net sellers at NT$-4.33B.
The TAIEX closed at 44,737.95 on Tuesday, down 1.42%, as renewed U.S.-Iran tensions and Monday’s 4.78% drop in the Philadelphia Semiconductor Index hit Taipei. Foreign investors sold a net NT$51.89 billion, with TAIFEX settlement Wednesday and TSMC earnings Thursday.
The TWSE suspended all trading Friday as Typhoon Bavi approached Taipei, freezing the tape at Thursday’s close: TAIEX 45,354.61, down 0.83% on the day and 3.05% on the week, with foreign investors selling NT$47.25B into the break.