[Edaily Reporter PARK MIN ] The formula “SamsungElectronics and SK hynix rise = KOSPI rises,” which has defined the domestic stock market since the start of the year, is beginning to waver. Last month, while SamsungElectronics(005930)and SK hynix(000660)fell in tandem, the KOSPI index rose by more than 3%, signaling a trend of “decoupling.” This is interpreted as a result of a “rotation in the market,” where liquidity that had been concentrated on the top two semiconductor companies is spreading to “non-semiconductor” sectors related to artificial intelligence (AI) infrastructure.

According to the Korea Exchange on the 2nd, SK hynix fell 2.56% from 1,718,000 won (based on the KRX closing price on July 31) to 1,674,000 won over the month of August. SamsungElectronics dropped 0.95% from 262,500 won (based on the closing price on July 31) to 260,000 won.

In contrast, during the same period, the KOSPI index rose 3.40%, from 6,595.45 to 6,820.02. The index actually showed a steady upward trend despite the simultaneous weakness of SamsungElectronics and SK hynix—the two stocks that account for the overwhelming majority of the KOSPI’s market capitalization (a combined 48%).

Industry analysts attribute this to a “rotational trading pattern,” in which liquidity previously concentrated on the two leading semiconductor stocks has spread across the broader market, and stock price gains are rotating among different sectors.

Baek Chan-kyu, Head of the Asset Management Consulting Center at NH INVESTMENT & SECURITIES, stated, “Fundamentally, when leading stocks lose momentum, the stock market enters a rotational trading phase.” He added, “The recent pattern—where sectors with strong earnings and high future value have taken turns rising while SamsungElectronics and SK hynix undergo a correction—can be viewed as a classic example of a rotational trading phase.”

In fact, the “KOSPI 200 Ex-Large-Cap Index”—which excludes mega-cap stocks like SamsungElectronics and SK hynix, which have a significant impact on the calculation of the KOSPI 200 Index, the benchmark for the Korean stock market—rose by 9.05 percent. Center Director Baek said, “We should view this as a shift in the market’s structure from a system relying on a single ‘major pillar’ to one supported by ‘multiple pillars.’”

In particular, “KOSPI mid-cap stocks”—which are smaller than large-cap stocks and thus experience much greater price volatility—rose 13.14%, while “KOSPI small-cap stocks” rose 10.10%. The KOSPI Mid-Cap Index comprises stocks ranked 101st to 300th by market capitalization, while the KOSPI Small-Cap Index includes all stocks ranked 301st or lower by market capitalization.

By sector, the construction index posted the largest gain, rising 27.98%, followed by chemicals (+17.18%), machinery and equipment (+14.38%), and metals (+13.74%). This is interpreted as capital flowing into upstream and downstream industries—such as AI data centers and power and power generation infrastructure—while the two leading semiconductor stocks underwent a correction.

Center Director Baek Chan-kyu explained, “Construction, chemicals, steel, and machinery are sectors set to benefit from the expansion of general AI infrastructure.” He added, “Construction stocks rose due to concentrated benefits from the groundbreaking of large-scale domestic semiconductor clusters, while battery companies within the chemical sector saw strong stock performance driven by data center energy storage systems (ESS), and machinery and equipment stocks were buoyed by factors such as semiconductor components and power generation engines.”

He continued, “The stock market typically shows seasonal weakness in September, and there is a lack of clear upward momentum to strongly drive the market.” He added, “With international oil prices rising sharply recently and U.S. Treasury yields showing no signs of falling easily, it is highly likely that we will see continued rotational trading focused on stocks with strong earnings or future value stocks, rather than a sharp rebound in blue-chip stocks.”