South Korea's stock market is crashing as fears about Chinese chip technology hammer Samsung, SK Hynix, and chip stocks worldwide — bad for chip investors, and the fear may spread to the US.

• Korea's main index fell so fast that trading was frozen multiple times, with big names like Samsung and SK Hynix down double digits in a single day.
• The trigger: a report that China is building its own chip-making machines, which could break the near-monopoly held by ASML and undercut Korean and Western chipmakers on price.
• China may make a handful of these machines this year and more next year, and it has been poaching Korean engineers for years to catch up.
• The Korean market had soared all year on heavy borrowing, so it now swings wildly up and down like crypto — still up sharply for the year despite the crash.
• Warning signs are piling up in the US too: Tesla's margins are shrinking and Google just went cash-flow negative, raising doubts about whether all the AI spending will pay off.

Outlook: The selloff is likely to spread from Korea to US tech and chip stocks as China's cheaper technology rattles the whole industry.