A full-stack AI-infrastructure selloff hit every US rung of the compute basket — semicap, optics, packaging and datacenter power all down double digits — while the memory strait held, with SK hynix the only gainer in its own Seoul session.

The leader was SK hynix (000660.KS), up 4.4% to ₩1,277,000 in its most recent Seoul session, on the HBM-and-memory-bandwidth chokepoint — the tightest single strait in the AI stack. This was a home-market move on its own calendar, decoupled from the US tape: the stock rose in Korea even as Wall Street's AI-infrastructure complex was routed, and it reports Q3 on October 29, so Thursday's gain was positioning ahead of what consensus expects to be another record HBM quarter, not a settled print. It was the only gainer of consequence among the basket's tracked names — in the US session the memory rung fell with everything else, Micron (MU) −6.3% to $856.49.

The laggard was FormFactor (FORM), down 15.3% to $95.03 on the metrology-and-test chokepoint — the probe cards that gate wafer-level validation of every accelerator and HBM stack. There was no company print (FormFactor reports October 28); this was the highest-beta test name in a sector-wide collapse. Thursday was a broad AI-trade derisking — the Nasdaq Composite fell 2.60% to 26,008.86 and the Philadelphia Semiconductor Index dropped 6.7% — triggered by revived bubble doubts and a Lam Research warning that chip-supply constraints could persist through 2027.

The selloff was uniform across the vertical's rungs. Semicap equipment was crushed: Lam's own peers Lam Research −11.8%, KLA (KLAC) −9.5% to $147.83, Applied Materials (AMAT) −8.2% to $375.58, Onto Innovation (ONTO) −10.6% to $198.67, Camtek (CAMT) −10.2% to $119.48 and Entegris (ENTG) −13.1% to $128.31 on materials, with ASML (ASML) −6.9% to $1,560.54. Optical interconnect fell as hard: Credo (CRDO) −10.7% to $162.77 and Lumentum (LITE) −11.5% to $752.54. Advanced packaging, the back-end bottleneck that gates HBM stacking, followed — Amkor (AMKR) −10.7% to $39.05 and ASE (ASX) −11.0% to $37.74. The accelerator anchors were comparatively resilient: NVIDIA (NVDA) −4.4% to $212.21, Broadcom (AVGO) −4.3% to $323.24, TSMC's ADR (TSM) −4.5% to $412.35 and Marvell (MRVL) −8.7% to $223.47, while hyperscaler Meta (META) −7.0% to $648.85.

The day's sharpest structural signal was the datacenter-power rung, the binding physical constraint on compute. It sold off with the AI complex rather than against it: GE Vernova (GEV) −10.6% to $827.42, Vistra (VST) −9.8% to $140.83, Vertiv (VRT) −7.8% to $195.59 and Constellation (CEG) −5.7% to $255.21 — a coordinated unwind of the "AI power" trade, not any one company's news (GE Vernova reports October 28). The near calendar now hangs on two memory and foundry gates: SK hynix's October 29 print, the first confirmation of whether the bandwidth strait is still tightening, and the year-end window for Intel's 14A external-customer decision. Until the memory read lands, the power and packaging rungs — not raw accelerator demand — will keep carrying the session-to-session tape.