A Japanese individual investor living in Tokyo posted the numbers showing in his securities account on social media.
The valuation of a single SK hynix holding was about 9.4 billion won, with a return of 720%. For some, it is a sum difficult to reach even after a lifetime of saving, and it has been created by betting on one Korean semiconductor company. The post has quickly spread among investors in and outside Korea.
The person drawing attention is a Japanese retail investor identified as A. On the 13th, he disclosed his brokerage account screen on his X account along with a post saying he had reached total assets of 1 billion yen. The screen showed an SK hynix holding valued at about 993.69 million yen. A said, “From June 2024, I invested 96.5% of my assets in SK hynix,” adding that “as a result, my assets increased eightfold.”
A return of 720% is striking, but behind it are conditions that ordinary investors cannot easily replicate and lessons worth reflecting on. It is not something to end with simply thinking, “I should have gone all in on SK hynix too.”
◆ From 216,000 won to 1.976 million won
In June 2024, when A began accumulating SK hynix shares, the stock was trading in the 230,000 won range. His average purchase price is known to have been about 216,000 won.
Although the HBM market for AI use was just beginning to open in earnest, doubts remained strong in the market about the sustainability of the memory semiconductor cycle.
Nearly two years later, on May 13, SK hynix closed at 1.976 million won, up 7.68% from the previous day. During the session, it climbed to 1.99 million won, setting a new all-time high. By simple calculation, that is more than a ninefold rise. On the same day, the KOSPI also set a new record closing high at 7,844.01.
It is hard to deny that A was fortunate. However, it is important to note that he was not merely an investor relying on luck. He has introduced himself as a 10-year veteran programmer, and after examining the structure of the AI semiconductor market, he judged that Korean memory companies stood at its center.
His use of Japan’s tax-free investment account, the NISA scheme, to also invest in Micron Technology and Samsung Electronics suggests that he was looking at the broader semiconductor industry structure.
◆ The conditions hidden behind a 720% return
Media outlets often highlight investors who made profits. Investors who lost money during the same period do not appear in the article. This is what statisticians call survivor bias. There may be many more cases of people pouring 96.5% of their assets into a single stock and suffering losses, but their stories do not become public.
The risk of concentrated investing is mathematically clear. Putting 96.5% of your assets into one stock means that if that stock is halved, total assets fall by about 48%.
It may only take a few days for a valuation of 9.4 billion won to shrink to about 5 billion won. Memory semiconductors are historically a cyclical industry where booms and busts alternate violently.
We should not forget that from the second half of 2022 through 2023, SK hynix posted operating losses exceeding 400 billion won per quarter.
A took a cautious stance regarding his investment approach. In response to remarks such as, “Is your next goal 3 billion yen?”, he said, “I don’t have a special goal,” and added that “going forward, I will gradually shift to diversified investing and aim for stable management.” The fact that the person who achieved the biggest gains is now turning toward diversification is meaningful.
Viewed from another angle, A’s caution can also be interpreted as meaning that he has already begun to weigh downside risk more heavily than the possibility of further upside for SK hynix. It may be a sign that the bet that generated a 720% gain is nearing its end.
◆ Why Korean retail investors cannot simply follow Japanese investors
The timing of A’s investment in SK hynix made it practically impossible for Korean retail investors to follow with the same level of allocation. During the same period, Korean investors moved in large numbers into U.S. big tech stocks. Nasdaq returns looked more attractive than the KOSPI.
The reason a foreign investor betting on a Korean stock became a sensation contains a paradox: while Koreans were turning away from their own flagship semiconductor company, a Japanese investor stepped in and captured a ninefold gain.
On the 13th, when SK hynix broke above 1.97 million won, foreigners sold a net 375.73 billion won worth of KOSPI shares. It was the fifth consecutive trading day of net selling. The gap was filled by individuals buying 188.47 billion won and institutions buying 169.17 billion won.
The question now is whether it makes sense to newly invest more than 90% of one’s assets in SK hynix at this point.
The difference between A’s average purchase price of 216,000 won and the 13th closing price of 1.976 million won is not just a number. Even in the same stock and the same company, the result of the same bet changes completely depending on the entry price. For late entrants, the same stock effectively becomes a different stock.
◆ Where is the AI semiconductor cycle now?
A said regarding the outlook for the AI semiconductor market that “the investment trend of major information technology companies is important,” and that “there is a possibility that investment will continue in 2027.” However, he also added the caveat that the pace of investment growth could slow. That means he does not believe the boom has ended, but neither does he think it will continue forever.
The securities market is repeatedly raising SK hynix’s target price. But target prices always lag behind the stock price. The pattern of target prices rising after the stock rises and falling after the stock declines has repeated throughout the semiconductor cycle. Korean investors experienced twice, in 2017 and 2021, that the moment when buy ratings piled up most heavily was often near the top.
The key to A’s ninefold return was not simply “buying SK hynix,” but “buying it in June 2024.” Timing mattered more than stock selection.
What Korean investors need is not to follow the same stock he bought, but to retrace the thought process behind why he chose that stock at that time.
As A now shifts toward diversification, the question posed to Korean investors becomes clearer. No one can answer whether SK hynix at 1.97 million won marks the end of a ninefold rise or the beginning of another leg higher.
One thing is certain, however: making a decision to place more than 90% of one’s assets into a single stock at 1.97 million won is a completely different game from making that decision at 216,000 won.