A Wall Street celebration turns into a Seoul hangover

Sometimes the same party looks very different depending on which side of the Pacific you're standing.

SK Hynix's 000660 long-awaited US market debut was met with cheers on Friday, with its American shares climbing 13% after the company's blockbuster $26.5 billion offering.

By Monday morning in Seoul, however, the mood had flipped. Shares of the South Korean memory-chip giant tumbled more than 15%, the worst single-day showing in its history, dragging the benchmark Kospi KOSPI down more than 9% and even triggering a brief circuit-breaker halt — a temporary pause in trading designed to calm markets during unusually sharp moves.

The reversal puzzled traders. How could a successful US debut be followed by such a painful selloff at home? As it turns out, the answer has less to do with panic and more to do with market mechanics.

???? Profit Taking Isn't Always Bad News

One of the biggest explanations is profit raking taking — a Wall Street term that simply means investors decide to cash in after a strong run.

And what a run it's been.

SK Hynix shares 000660 have surged more than 25-fold since late 2022 as artificial intelligence transformed memory chips from a relatively sleepy business into one of the hottest corners of the semiconductor industry.

Just ask Micron MU and Sandisk SNDK , especially Sandisk.

Against this backdrop, Hynix has become one of Nvidia's NVDA most important suppliers of high-bandwidth memory (HBM), the ultra-fast chips that help AI systems process enormous amounts of data.

After years of gains, a successful US listing gave many Korean investors a convenient moment to lock in profits. Others shifted their holdings into the newly listed American depositary receipts, creating additional selling pressure on the Seoul-listed shares.

???? Wait... Was This an IPO?

Not really.

While many headlines compared the debut to an IPO, Hynix didn't go public in the United States because it was already a publicly traded company in South Korea.

Instead, it launched American Depositary Receipts (ADRs) under the ticker $NASDAQ:SKHYV (but that will change to SKHY on Tuesday).

Think of an ADR as a wrapper that allows US investors to buy shares of a foreign company on an American exchange without purchasing the original stock overseas. A bank holds the underlying Korean shares and issues tradable receipts in the US.

An IPO, by contrast, is when a company sells shares to the public for the very first time. SK Hynix has been public for years — it simply opened another door for investors. Here’s a nice IPO calendar for reference.

???? AI's Favorite Memory Maker

The offering was closely watched because it tested two things at once: global appetite for overseas listings and investors' confidence that the AI boom still has legs.

Demand certainly showed up. The deal was reportedly more than seven times oversubscribed, even as some investors questioned whether AI-related valuations have climbed a little too far, too fast.

Hynix sits at the center of that story. Alongside larger rival Samsung Electronics 005930 (down more than 10% on the day), it manufactures memory chips used in everything from smartphones to data centers.

As AI models grow better, faster, stronger, demand for faster memory has exploded, helping drive record profits across the industry.

⚖️ The Bigger Question

For all the excitement, investors are beginning to ask a familiar question: what happens when everyone builds more factories?

Hynix chief executive Kwak Noh-Jung believes memory shortages could persist well beyond 2030, suggesting demand will remain robust for years.

Still, expanding production has historically been a double-edged sword. Memory chips have long been a cyclical business, where periods of shortages eventually give way to oversupply, squeezing prices and profits.

That uncertainty has made Hynix one of Korea's most volatile stocks. Leveraged ETFs tracking the company have amplified market swings, contributing to an unusually high number of trading halts on the Kospi this year — seven times already, out of 13 since 2000.

With Hynix shares already down more than 30% from their June peak, the market seems to be in limbo on the proper price tag.

Off to you: What do you think of the AI craze? Overvalued or nah?