SEOUL, Sept 1 — Shares in SK Hynix and Samsung Electronics dropped today after Washington revoked authorisations that allowed them to secure US semiconductor manufacturing equipment for their chip plants in China.

The two chipmakers had, until now, benefited from exemptions to sweeping restrictions that the US has imposed on chip-related exports to China. The move is set to go into effect in 120 days.

The South Korean chipmakers dominate the global production of memory chips. Together they hold about 70 per cent of the DRAM market, a key type of chip powering data centres and artificial intelligence, as well as 54 per cent of the NAND market.

Shares in SK Hynix slid 5 per cent. Analysts estimate that 30 per cent to 40 per cent of its DRAM and NAND production is based in China.

Samsung is seen as less affected, with only NAND production located in China, although it is still sizeable at roughly a third. Its shares fell 2.6 per cent.

Ryu Young-ho, a senior analyst at NH Investment & Securities, said he thought the short-term impact would be limited.

“Samsung and SK Hynix have planned their new production lines and processes primarily in South Korea, while maintaining the status quo in China,” he said. But he added that Washington’s action could benefit rivals like Micron, which rely less on China for their production sites.

In response to the move, SK Hynix said it would maintain close communication with both the Korean and the US governments and take necessary measures to minimise the impact on its business.

Samsung declined to comment.

Analysts also said the two companies might expand partnerships with Chinese equipment makers to better stabilise their operations in China if US machinery is not secured in time.

Shares in other South Korean chip assembly and product suppliers also retreated today on concerns that they too would be affected. Hana Micron fell 2.2 per cent and Hanmi Semiconductor dropped 4.8 per cent.

US President Donald Trump has also threatened a 100 per cent tariff on imports of semiconductors. While Samsung and SK Hynix could be spared due to an expected exemption for companies investing and building factories in the United States, the tariffs would most likely disrupt a complex and global supply chain. — Reuters