Two Semiconductor Giants Approach Half of KOSPI

The combined market capitalization of Samsung Electronics and SK Hynix surpassed 40% of the entire KOSPI for the first time on the 18th. As of market close, Samsung Electronics' market cap reached 1,234.2 trillion won, accounting for 25.22% of the total KOSPI (4,892.8 trillion won), while SK Hynix stood at 752.6 trillion won, representing 15.38%. Combined, the two companies totaled 1,986.9 trillion won, amounting to 40.61% of the entire securities market.

Samsung Electronics closed at 208,500 won, up 7.53% from the previous trading day, while SK Hynix rose 8.87% to 1,056,000 won. Just five days earlier on the 13th, the two companies' combined KOSPI market cap weight was 38.3%.

Multiple Tailwinds Drive Surge

The sharp price increase resulted from several converging positive factors. Overnight in New York, Micron surged 4.5% ahead of its earnings announcement, creating upward pressure on domestic semiconductor stocks. NVIDIA's ongoing annual developer conference 'GTC 2026' also improved investor sentiment across the semiconductor sector.

Particularly significant was Samsung Electronics' announcement at its regular shareholders' meeting of a 16 trillion won share buyback and cancellation in the first half, along with an additional 1.3 trillion won in dividends, which fueled shareholder return expectations. Nomura Securities' upward revision of Samsung Electronics' target price from 290,000 won to 320,000 won—its second increase in a month—also stimulated buying interest.

Lee Kyung-min, a researcher at Daishin Securities, analyzed: "Samsung Electronics confirmed a virtuous cycle where recent earnings improvements lead to enhanced shareholder returns. NVIDIA CEO Jensen Huang's hints at potential collaboration with Samsung Electronics and expressions of gratitude at GTC further improved investment sentiment across the semiconductor sector."

Weight Nearly Doubles in One Year

The concentration in large-cap stocks has intensified dramatically in recent months. The two companies' combined KOSPI market cap weight was just 23.7% in March last year, but has nearly doubled in approximately one year. During the same period, the ratio of the top 10 stocks by market cap expanded from 41.1% to 51.7%.

Jung Yong-taek, a researcher at IBK Securities, pointed out: "Compared to the U.S. S&P 500, where the top two stocks account for just over 10%, Korea's reality of two semiconductor stocks comprising 40% is a key factor amplifying index volatility."

The two companies also maintain solid positions in global market cap rankings. As of the close of regular trading on the Korea Exchange, Samsung Electronics' global market cap ranking rose one notch to 13th, while SK Hynix at 22nd is closely chasing Micron at 21st.

Structural Challenges Facing Korean Markets

The surge in these two companies' market cap weight reveals structural characteristics of Korea's stock market. With the semiconductor industry as a core pillar of the national economy and a main export driver, a structure is solidifying where global semiconductor market booms propel the entire domestic market.

The problem is that this concentration amplifies index volatility. While KOSPI surges when semiconductor conditions improve, the entire market can suffer significant damage when conditions deteriorate. Critics note that Korea's market shows relatively insufficient sector diversification compared to U.S. markets.

Industry observers evaluate this rally as the result of two factors converging: expectations of semiconductor industry recovery and enhanced shareholder returns, going beyond a simple stock price rally. The future trajectory of both companies' stock prices will depend on Samsung Electronics' foundry business recovery and the sustainability of SK Hynix's high bandwidth memory (HBM) demand.