[Edaily Reporter PARK MIN ] The formula “Rises in SamsungElectronics and SK hynix = Rise in the KOSPI,” 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 the result of a “rotation in the market,” where liquidity previously concentrated on the top two semiconductor stocks 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 during the month of August. SamsungElectronics declined 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 overall KOSPI index rose 3.40%, from 6,595.45 to 6,820.02. Even though SamsungElectronics and SK hynix—which together account for an overwhelming 48% of the KOSPI’s market capitalization—both posted losses, the index actually showed a steady upward trend.

Industry analysts attribute this to a “rotation-driven market,” in which liquidity that had been concentrated on the top two 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, said, “Fundamentally, the stock market enters a rotational trading phase when leading stocks lose momentum,” adding, “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 typical rotational trading phase.”

In fact, the “KOSPI 200 Ex-Megacaps Index”—which excludes megacap stocks like SamsungElectronics and SK hynix, which have a significant weighting in the KOSPI 200 Index—rose by 9.05%. 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 energy 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 significantly 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.”