SUMCO CORPORATION finished selling part of its stake in Formosa SUMCO Technology Corporation (FST) on Taiwan's stock market on August 20, 2026, cutting its voting rights in the Taiwanese wafer maker to 38.0%. That is below the level needed to keep FST inside SUMCO's consolidated accounts, so the Taipei-registered supplier now moves to equity-method treatment.
The sale was carried out by SUMCO TECHXIV, a SUMCO subsidiary, on the Taiwan stock market. SUMCO's extraordinary report to the Kanto Local Finance Bureau puts the immediate pre-sale position at 157,742,849 voting rights, or 40.7%, falling to 147,382,862 rights, or 38.0%, after the transaction. A separate notice tied to SUMCO's original February 19 announcement of the planned sale had cited a 43.2% starting point, reflecting the ownership level at the time that plan was first disclosed rather than the position immediately before this specific trade. Both disclosures agree on the same post-sale figure: 38.0%.
| Disclosure | Before Sale | After Sale |
|---|---|---|
| EDINET extraordinary report (position immediately before this trade) | 40.7% (157,742,849 voting rights) | 38.0% (147,382,862 voting rights) |
| TDnet notice (position as of the original Feb 19, 2026 plan announcement) | 43.2% | 38.0% |
For accounting purposes, SUMCO will treat the change as taking effect on September 30, 2026, the close of its third quarter, using deemed-transaction accounting rather than the actual August 20 trade date. From that point, FST's results roll into SUMCO's consolidated financials through the equity method instead of full consolidation. SUMCO said the earnings impact on its current fiscal year is still being assessed and it will disclose further details if anything material emerges.
FST remains capitalized at NT$3,878mn and continues making and selling semiconductor silicon wafers from its base in Taipei. It is a joint venture with Taiwan's Formosa Plastics Group, and SUMCO said the two companies will keep working together on production and sales even after the ownership change, while continuing to review what capital structure best serves FST's corporate value. One change already in effect: the number of SUMCO-affiliated directors on FST's board has dropped by one.