September 2025 in returns

September 2025 is the month the memory cycle announced itself, and in hindsight it is the most consequential month in this record. Sandisk gained 113.8%, Western Digital 49.6%, Seagate 41.5% and Micron 40.6% — storage and memory, all four, moving together — with Nebius (+64.3%), Ciena (+55.0%) and AppLovin (+50.1%) alongside. That quartet is not a coincidence or a squeeze; it is the market pricing a physical shortage. Everything that followed for the next ten months, up to and including July 2026's unwind, traces back to what began here.

The rest of the month was orderly. The Nasdaq rose 5.6%, the S&P 500 3.5%, Nvidia 7.1%, with 531 of 869 stocks (61%) green, and gold gained 11.8% — its strongest month in this record, and a strange companion to an equity advance. Crypto was mixed and thinning: Bitcoin +5.4%, Ethereum -5.6%, 71 of 169 coins (42%) green. The equity losers were defensive and dull — FactSet -23.3%, Kenvue -21.6%, Synopsys -18.2%, Constellation Brands -16.8% — which is the correct backdrop for a month whose real content was a supply shock forming in one narrow corner of the market that almost nobody was looking at yet.