The memory supply chain split at both ends — SUMCO's silicon wafers surged ~15% in Tokyo on Friday while SK hynix's HBM line fell a record 15.4% in Seoul on Monday — as Meta and Nvidia led the US tape.

SUMCO's US line (SUOPY) rose 13.6% to $65.67, mirroring a 15.4% surge in the Tokyo ordinary (3436.T, to ¥5,244) in Friday's session — the largest single-stock advance on the Nikkei that day. SUMCO is the world's second-largest maker of 300mm semiconductor-grade silicon wafers, and the move rode a hardening wafer-shortage narrative and pre-earnings buying: the mainstay substrates feed GPUs, HBM stacks, CPUs and NAND alike, so a tightening here is the most upstream chokepoint in the entire AI build-out. Shin-Etsu's US line (SHECY), the wafer leader, firmed roughly 4% alongside it.

At the other end of the memory chain, SK hynix (000660.KS) fell 15.4% to ₩1,845,000 in Monday's Seoul session — its largest one-day drop on record, from ₩2,180,000 at Friday's close. The catalyst was a reversal of last week's euphoria: SK hynix's Nasdaq ADR (SKHY) had surged about 13% in its blockbuster Friday debut off the roughly $26 billion offering, and Monday brought profit-taking, valuation-arbitrage between the new US line and the Korean stock, and the dilution mechanics of that share issuance — compounded by caution that the Q2 ramp of HBM4 shipments has not materialized at scale. HBM is the memory chokepoint on AI training; this was the tape re-pricing how tight it really is.

The US session on Friday leaned green at the leading edge. Meta (META) jumped 6.0% to $669.21 on plans for a "Meta Compute" cloud unit and its in-house "Iris" accelerator with Broadcom and TSMC — a demand-side signal that hyperscaler silicon spend keeps widening. Nvidia (NVDA) added 4.0% to $210.96 on Morgan Stanley's reaffirmed Overweight, and SoftBank (SFTBY) +4.1%, Applied Materials (AMAT) +2.4% to $602.50, Lumentum (LITE) +2.1% and Besi (BESIY) +1.6% followed. The decliners were interconnect and packaging: Marvell (MRVL) −3.1% to $235.81, Credo (CRDO) −3.0%, Amkor (AMKR) −2.3% and Micron (MU) −1.2% to $979.30.

The hard reads now arrive in a rush. ASML reports July 15, TSMC July 16, Intel and Samsung July 23, Amkor July 27, Alphabet and Microsoft July 28, and SK hynix's own Q2 — freshly scrutinized after Monday's rout — on July 29, with Entegris July 30. Each tests a different link: leading-edge tools, foundry demand, memory pricing and HBM4 timing. After a week that saw wafers bid and HBM broken, the chokepoint map has rarely been more legible.