Samsung Electronics share price graph shows on a Yonhap Infomax electronic board at the Yonhap News Agency headquarters in Jongno-gu, Seoul, on Thursday. (Yonhap)

Samsung Electronics, South Korea’s largest chipmaker, has seen its market cap shrink by a staggering 90 trillion won ($66.6 billion) since September, largely driven by a sustained selling spree among foreign investors.

According to the Korea Exchange on Sunday, foreigners have net sold 10.6 trillion won in Samsung Electronics shares over the past month, marking 23 consecutive days of selling since Sept. 3 -- just two days shy of the record 25-day selling streak set in 2022.

During this period, Samsung’s share price dropped 20.3 percent, from 74,400 won to 59,300 won, far outpacing the Kospi's market average 2.9 percent decline.

Foreign investors, who had been net buyers of 10.76 trillion won in Samsung Electronics during the first seven months of this year, reversed course sharply, unloading a net 12.65 trillion won since August.

Foreign ownership of the company’s shares fell by 2.27 percent, from 56.02 percent at the end of August to 53.75 percent by the end of September -- the steepest monthly drop in 20 years.

Samsung Electronics’ stock slide has been exacerbated by weaker-than-expected earnings. This week, the company estimated its third-quarter operating profit at 9.1 trillion won, falling short of the brokerage consensus of 10.77 trillion won. Sales are projected to hit a record 79 trillion won, but that figure is still below the market expectation of 80.9 trillion won.

Meanwhile, Samsung Electronics' domestic rival, SK hynix, has fared better. Foreigners have net bought 328.76 billion won in SK hynix since Sept. 3, the most of any Kospi stock, signaling confidence in Korea’s second-largest chipmaker despite broader industry pessimism.