Two sessions of oil and yields take back 39% of the KOSPI's weekly advance

The KOSPI ended at 6,909.91, up 3.33% for the week ^[4], which puts the starting point near 6,687.13 ^[1]. The run to 7,051.64 on the 9th ^[2] was therefore 364.51 points ^[2], and the two-day retreat was 141.73 ^[3]. That is 2.0% off the peak and about 39% of the week's advance ^[3][4]. The give-back came as renewed US-Iran military conflict pushed oil prices and Treasury yields sharply higher ^[1].

Foreigners sold a net 1.4391 trillion won of Samsung Electronics ^[13] and 1.2074 trillion won of SK hynix ^[14]. The pair comes to 2.6465 trillion won ^[5]. Total foreign net selling on the main board was 2.1259 trillion won ^[11], so foreigners were net buyers of roughly 520.6 billion won of everything else ^[6]. Retail investors were the bigger seller, at 9.9104 trillion won ^[11]. On the other side sat 8.4906 trillion won of net purchases by other corporate entities, reflecting buybacks at Samsung Electronics and SK hynix ^[12]. That covered 70.5% of the combined retail and foreign selling ^[7].

Friday's session separated the two stories. All three major US indexes advanced together for the first time in five sessions ^[8], and crude fell, Brent by 2.81% and WTI by 2.37%, after reports of talks between Iran and Gulf states over the Strait of Hormuz ^[9]. The Philadelphia Semiconductor Index rose 1.81%. Micron fell 0.22%, SanDisk 3.50%, Western Digital 2.98% and Seagate 3.73% ^[16]. The reasons given for the memory weakness were DeepSeek's low-cost model, which sharply reduces high-bandwidth memory use, and the market debut of Chinese GPU maker Enflame ^[17]. The MSCI Korea Index ETF rose 3.25% and KOSPI200 night futures gained 0.97% ^[10].

Samsung Securities said higher oil prices and yields would cap the market's upside while AI investment and rising corporate profits would support the downside ^[20]. "If a rate increase is carried out, inflation expectations may ease, and the stock market could well take it as a removal of uncertainty," said Kim Jong-min, senior research fellow at the firm ^[21]. Mirae Asset Securities said a 5% 10-year yield was not by itself a threshold for a financial crisis, but that differentiation would widen between companies able to absorb higher capital costs and those that cannot ^[22]. "We maintain a positive view on semiconductors as long as AI memory demand and earnings improvement continue, but in a high long-term rate environment, profit growth needs to be at the center of investment returns," said Kim Seok-hwan, an analyst at Mirae Asset Securities ^[23].

In my view the crude spike is the smaller of the two problems here, because it reversed within days ^[9], while the DeepSeek release is a claim about how much high-bandwidth memory each unit of AI output needs ^[17], and that is the product Samsung and SK hynix sell. If the quarter-point increase the market is pricing at better than 80% odds ^[18] eases inflation expectations, the 10-year steps back from 5% ^[6] and the chip trade resumes on the Astra demand story that started it ^[3]. Or the Red Sea route stays contested, oil holds above $100 ^[5], and rates cap the index whatever memory demand does ^[20]. Memory names recovering while the 10-year sits near 5% would say last week's drawdown was an oil trade; memory lagging a falling crude price would say DeepSeek is being priced into memory volumes.