Samsung Electronics Co. and SK Hynix Inc. are close to completing their combined 55 trillion won ($40.5 billion) share buyback program, originally slated to run through the second half of November. According to Bloomberg calculations based on exchange data, roughly 80% of the repurchases have already been executed, and at the current pace the buying could conclude by mid-October — about a month ahead of schedule.

The accelerated purchases have served as a crucial source of demand for the benchmark Kospi index, particularly as trading volume has dried up and few other large buyers have emerged. With the support set to disappear earlier than expected, the index may become more reliant on a revival in foreign and institutional investment to break sustainably above the 7,000 level that has held since late July.

"As the pace of the buyback was faster than expected, I think it will be exhausted by mid- or end-October," said Cho Junkee, an analyst at SK Securities. "When the buyback is gone, it could be a factor that somewhat elevates volatility."

The buybacks form part of the largest shareholder return program in South Korea’s history, launched amid investor pressure to distribute more cash generated by the AI boom. Despite foreign investors selling about $14 billion of Kospi stocks in September and retail investors offloading $11 billion, the index is still on track to end the month nearly flat thanks to the chipmakers’ purchases. However, the Kospi has lost almost 20% this quarter, marking the worst performance among major equity benchmarks.