Samsung Electronics and SK Hynix, South Korea's two giant chipmakers, have lost a combined 2,261 trillion won in market value since 22 June, as the global sell-off in artificial intelligence stocks has wiped out more than half of their worth in less than five months.

According to Korea Exchange data, Samsung Electronics has lost 996 trillion won, or 48.18%, of its market value since 22 June, while SK Hynix has lost 1,265 trillion won, or 60.81%. Their combined market value has fallen from 4,147 trillion won to 1,886 trillion won, a decrease of about 54.52%. Their share of the total market capitalisation of the KOSPI has dropped from 55.7% to 46.5% over the same period.

The slide mirrors the fall of the wider market. The KOSPI has dropped from its record closing high of 9,114.55 points on 22 June and briefly fell below the 5,000 level during the rout, a stunning reversal for an index that had been the world's best performing major benchmark for much of 2026.

The heaviest single day came on 5 November, when the two companies shed a combined 192.89 trillion won in market value in one session. Samsung Electronics closed at 201,500 won, down 7.57%, while SK Hynix finished at 1,264,000 won, down 9.46%. The two companies lost almost identical amounts that day, 96.46 trillion won at Samsung and 96.43 trillion won at SK Hynix.

The KOSPI closed at 5,383.80 on 5 November, down 300 points, or 5.28%, from the previous session, according to the Korea Exchange. It was the first close below 5,400 since 3 April, when the index finished at 5,377.30. The KOSDAQ ended at 678.41, down 36.54 points, or 5.11%, slipping into the 600s for the first time in about three months.

South Korean stocks tumbled on fears that the Democrats' victory in the US midterm elections will bring tighter regulation of artificial intelligence data centres. Investors worried that even if long-term investment plans hold, tighter regulation could delay permits and slow growth in semiconductor demand, undercutting the memory chip boom that had powered the two companies' shares to record highs.

Foreign investors sold a net 3.42 trillion won worth of shares on the KOSPI alone on 5 November, extending their selling streak to a fifth session. Chip equipment makers and other stocks across the AI value chain were hit as well, as the selling spread beyond the two memory giants.

The Korean sell-off stood in sharp contrast to US markets that day, where the Dow Jones Industrial Average surged as investors focused on reduced uncertainty after the midterms. Hyperscalers including Amazon and Microsoft advanced on expectations that a slower pace of data centre investment would ease capital expenditure burdens. Oil prices fell on hopes for an end to the war in Iran, while Treasury yields and the dollar weakened.

Analysts expect the volatility to persist. "Volatility is unavoidable for a while because memory chipmakers account for such a large share of the Korean market," said Min Jae-ki, head of KB Securities' Prime Club. "If the president counters the Democratic Party's policy push with vetoes, only the shares of companies with strong earnings may end up rising selectively."

For South Korea, the stakes are high. Samsung and SK Hynix dominate the global market for the high-bandwidth memory chips used in AI servers, and their shares had become the engine of the KOSPI's record run. Their collapse has now dragged the index down with them, and with their combined market value below 2,000 trillion won for the first time in about seven months, investors are watching whether the coming week brings stability or a fresh leg down.