SK Hynix plunges after Nasdaq debut as memory chip euphoria cools

July 13 (Reuters) - SK Hynix's Seoul shares posted their biggest one-day fall in nearly two decades on Monday, tumbling more than 15%, as investors unwound gains from a scorching rally following the company's Nasdaq debut last week.

The company's U.S.-listed shares dropped 7.9% to $154.7 in early trading after jumping more than 12% in their Nasdaq debut on Friday.

The declines in SK Hynix's shares, alongside those of rival chipmaker Samsung Electronics, contributed to a 9% plunge in South Korea's Kospi, triggering a 20-minute trading halt.

Shares of U.S. rivals also dropped. Micron Technology fell 6.4%, SanDisk 8.4% and Western Digital 6.8%. The broader Philadelphia SE Semiconductor index lost 3.6%.

Korean stocks extended losses after trading resumed after President Lee Jae Myung on Monday reiterated that the government would help speed up projects to build chip fabs in investments worth hundreds of billions of dollars, as outlined by Samsung and SK Hynix.

The world's leading AI memory chipmaker, SK Hynix, raised over $26 billion last week selling American Depositary Receipts priced at $149 each, after its Korean shares more than tripled this year. The ADRs opened 14% above the offer price at $170 before ending their first trading day at $168.

"We've had such a run up in (memory chip) stocks that there's obviously a component of profit taking but I don't think it's the end of the run," said Phil Blancato, president and CEO of Ladenburg Thalmann Asset Management.

"The demand cycle is still very strong and I don't think we're at the end of it yet. You're looking at demand for multiple companies out into late 2027, into early 2028."

Analysts have said the large-scale investments in Korea had heightened uncertainty over the supply outlook and fuelled concerns that the current period of tight supply could eventually give way to an oversupply cycle.

"Our base case here is the fresh capacity in 2027 and 2028 coming up in earnest will improve supply dynamics, thereby leading to price erosion," said Jing Jie Yu, an equity analyst at Morningstar.

SK Hynix Chief Executive Kwak Noh-jung dismissed concerns about aggressive capacity expansion, telling Reuters that the memory industry is heading for its most severe supply shortage in 2027, forecasting that demand will continue to exceed the company's ability to produce memory chips well into the next decade.

Chip stocks have had a rough start to the month of July, as investors wrestle with high valuations and question the longevity of the AI capex boom.

"Despite accelerating artificial intelligence adoption, monetisation remains uncertain and profitability for key players, such as OpenAI, appears to be under pressure," said Lorraine Tan, director at Morningstar.

"Funding is also shifting toward debt or equity, raising concerns about the maintainability of current spending levels."

Volatility in SK Hynix shares has surged this year as it has become a target of global investors betting on a sustained boost to profits from a shortage of high-bandwidth memory chips used in AI data centres, with many investors using leveraged exchange-traded funds that have amplified returns and losses.

In Hong Kong, a single-stock ETF tracking SK Hynix offered by fund manager CSOP, which uses leverage to target twice the daily returns of its shares, lost more than a third of its value on Monday, its biggest one-day decline since listing in October.

After the rout in the Seoul market on Monday, SK Hynix's U.S. ADRs, which represent one-tenth of a share and were last at $154.70 on Monday, were trading at a premium of about 25.6% to the South Korean share price.