[Spotlight] Resonac (4004) rises for 3 consecutive days, taking the top spot for price gains on the Prime Market! Major US investor increases stake—what happened to the stock …

What happened to Resonac yesterday

On Friday, October 2, 2026, the stock price of Resonac Holdings (4004) closed at 17,280 yen, up 1,385 yen from the previous day, an increase of +8.71%. It proudly took the top spot in the price gain ranking on the Tokyo Stock Exchange Prime Market.

On this day, the Nikkei Stock Average saw profit-taking, primarily in value stocks such as automobiles and retail, as a reaction to the sharp rise of over 3,400 yen in the two days leading up to it. This was a counter-trend rise while the overall market took a breather; it was not a case of “rising because the market is strong.”

The direct trigger is considered to be the revelation that the shareholding ratio of Resonac stock by Capital Research and Management, a subsidiary of the major US investment firm Capital Group, had increased from 11.62% to 12.40%. However, explaining it solely by that is a bit too simple.

In the background, multiple factors are piling up, such as the completion of the spin-off and listing of the petrochemical business, which has clarified its image as a “semiconductor materials company,” successive target price hikes by securities firms, and the major tailwind of AI demand.

In this article, after organizing yesterday’s price movements, I will explain in order the reasons for the rise, the position of the stock price, points to note, and future points of interest.

Yesterday’s stock price movement: A strong trend of rising from the low range toward the close

First, let’s organize the numbers. The closing price of the previous day (October 1) was 15,895 yen, and on October 2, it opened at 16,050 yen. The low was 15,985 yen immediately after the opening, and from there, the stock price climbed.

The morning session closed at 16,620 yen (+4.6% from the previous day), and even at this point, it was ranked first in the morning session’s price gain ranking. Entering the afternoon session, buying became even stronger, and it topped the 17,100 yen level in the 14:00 hour. And the closing price of 17,280 yen became the high for the day.

The points are the following three:

• Closing price is the same as the high: Buying continued toward the close, ending in a strong form where selling was difficult to emerge.
• Trading volume was approximately 4.24 million shares: It was a lively performance worthy of entering the top of the ranking.
• 3 consecutive days of gains: October 1 was +910 yen (+6.07%), and the 2nd was +1,385 yen (+8.71%). It rose about 15% from the closing price on September 30 (14,985 yen) to the closing price on October 2.

Compared to the recent low range, the momentum is even clearer. The closing price on September 28 was 14,695 yen, and from there, it rose about 17.6% in four business days. From the monthly low of 12,885 yen set on September 14, it is a recovery of about 34%.

It is natural to view such a rise not as “buying in a panic after seeing the news,” but as a movement where multiple good materials were recognized over several days, and then the material on October 2 overlapped, accelerating buying all at once.

What kind of company is Resonac?

Resonac Holdings is a chemical manufacturer born from the integration of the former Showa Denko and the former Showa Denko Materials (formerly Hitachi Chemical). In the past, it had a strong image as a “comprehensive chemical” company dealing in petrochemicals, graphite electrodes, and aluminum.

Currently, the company has placed semiconductor and electronic materials at the core of its growth. Particularly strong is the field called “back-end processing.” Semiconductors become products after front-end processing, where circuits are created on wafers, followed by back-end processing, where they are cut, mounted on substrates, and sealed. Resonac has a global share in the materials used in this back-end processing.

Representative examples are materials for sealing semiconductor chips and copper-clad laminates used for substrates on which chips are mounted. For high-performance semiconductors for AI, the difficulty of back-end processing is increasing, such as stacking multiple chips or mounting them on large substrates. As a result, demand for high-function materials is increasing, and pricing power is also rising.

In fact, the Nihon Keizai Shimbun reported in early September that Resonac is achieving high profit margins in semiconductor materials through price increases. The revenue for the semiconductor and electronic materials business for the fiscal year ending December 2026 is expected to increase by approximately 32% from the previous term, and core operating profit is expected to increase by approximately 80%.

In other words, the market is re-evaluating Resonac not as a “materials manufacturer swayed by the economy,” but as a “high-growth materials manufacturer related to AI.” This composition is the foundation of this stock price rise.

Reason for rise ①: Capital Research’s shareholding ratio increased

The direct material yesterday was the change report of the large shareholding report. According to documents submitted to the Kanto Local Finance Bureau, the shareholding ratio of Capital Research and Management and its joint holders increased from 11.62% to 12.40%. Capital Research alone holds 11.86%. The date the reporting obligation occurred was September 25, and the purpose of holding is stated as pure investment for overseas investment trusts that are clients.

One needs to be a little careful about how to read this information.

First, the increase in buying itself is a story as of September 25. It was not bought more on October 2, but the buying that had already been done was disclosed yesterday. The stock price reacted to “new information” rather than “new supply and demand.”

Second, the magnitude of the message that this “information” means. One of the world’s leading long-term management institutions holds a large ratio of about 12% and is further accumulating. Moreover, the purpose is pure investment, not participation in management. It is easily perceived that institutional investors have made the judgment that it is “worth holding for the long term.”

Third, the impact on the psychology of individual investors. On bulletin boards and the like, this report was cited first as a factor for yesterday’s rise. The sense of security that “if a large player is buying” attracts short-term funds.

However, an increase in the shareholding ratio does not guarantee future stock prices. Institutional investors buy sometimes and sell sometimes. It is strictly a good material on the supply and demand side, and it is necessary to look at it as a set with the backing of business performance.

Reason for rise ②: To a “semiconductor materials company” through the spin-off and listing of the petrochemical business

Another thing that cannot be overlooked is the change in business structure. On September 29, Kurasa Chemical (646A), which handles Resonac’s petrochemical business, was newly listed on the Tokyo Stock Exchange Standard Market through a partial spin-off (a form of separating while leaving a part).

Petrochemicals are easily affected by market conditions, and profits are difficult to stabilize. It is, so to speak, a “cyclical” business. By separating this, the Resonac main body can increase its concentration on semiconductor and electronic materials.

From an investor’s perspective, the following effects are expected:

• The view of the business becomes simpler: It becomes easier to evaluate the growth potential of semiconductor materials without the noise of the market-sensitive business.
• The yardstick for evaluation changes: There is a possibility that it will be viewed not by the PER of a comprehensive chemical company, but by the PER of a semiconductor materials company.
• Management resources can be concentrated: It becomes easier to direct investment and human resources to growth fields such as back-end materials.

On the other hand, attention is also gathering on Kurasa Chemical, which was separated. On October 2, it had a sense of being undervalued with a PBR in the 0.7x range and a dividend yield in the mid-5% range, and it was among the top in the number of buy predictions by individual investors. Due to the separation, a composition has been created where investors seeking growth are in the Resonac main body, and investors seeking yield are in Kurasa Chemical, dividing the investor base.

Note that stock price comparisons become complicated due to price adjustments around the spin-off. The numbers in this article use the stock prices displayed in the market as they are, but if you are making detailed comparisons, please check the adjusted stock prices.

Reason for rise ③: Successive target price hikes by securities firms

In the last few days, analyst evaluation revisions have also continued. On September 30, a mid-tier domestic securities firm maintained its bullish judgment and raised its target price to 22,800 yen. On October 1, Iwai Cosmo Securities also raised its target price. Both are based on the strength of semiconductor back-end materials.

Target price hikes bring a double effect to the stock price.

First, the creation of a sense of undervaluation. Against yesterday’s closing price of 17,280 yen, if the target is 22,800 yen, there is about 30% room for upside.

Second, the sense of security that “everyone is watching.” When multiple analysts change their evaluations in the same direction, it becomes material for buyers that “I am not the only one who is bullish.”

However, evaluations are split among companies. On a site that aggregates individual investor predictions, the target price is about 16,800 yen, which is lower than yesterday’s stock price. There is a temperature difference between the bullish view of securities firms and the current stock price level. Rather than thinking simply that “I will buy because an analyst raised it,” I want to check the underlying business performance outlook myself.

Reason for rise ④: Decision on supply provider for green ammonia demonstration

Around noon on October 2, another piece of news came out. Resonac announced that it would cooperate as a green ammonia supply provider in the “Development of Large-Scale Alkaline Water Electrolysis Hydrogen Production System and Demonstration of Green Chemical Plant,” which Asahi Kasei and JGC Holdings are promoting as a Green Innovation Fund project of NEDO (New Energy and Industrial Technology Development Organization).

Specifically, it will supply green ammonia to a thermal power plant in Fukushima Prefecture. At the power plant, it is scheduled to be used for flue gas denitrification.

However, it is difficult to say that this news was the main cause of the +8.71%. There are two reasons.

1. The time of the announcement was around noon, and the rise in the stock price had already started from the morning.
2. The scale of the business and its contribution to earnings are not large at this point.

Nevertheless, it is material that shows it is involved in the growth theme of “decarbonization,” and for buyers, it became an additional material that made them think “there are sprouts of growth here too.” It is appropriate to position it as a supporting role that boosted the momentum of the rise, not the lead.

Relationship with market conditions: A counter-trend rise while the Nikkei Average was falling in reaction

What makes yesterday’s rise stand out more is the movement of the market as a whole. The Nikkei Average rose over 3,400 yen in the two days leading up to October 1. As a reaction to that, on October 2, profit-taking selling took precedence, and SoftBank Group, Tokyo Electron, and Fast Retailing, which have a large contribution to the index, became factors for the decline.

On such days, the more a stock has risen recently, the easier it is to be sold. Among them, the fact that Resonac came to the top shows that the reason for buying was not “market momentum,” but individual materials and the flow of funds.

In a phase where the strength of individual stocks stands out, two views can be taken.

• Positive view: Being bought even when the index is weak is proof that investors have conviction in the company’s growth.
• Cautious view: Because funds are concentrated in a few stocks, the reaction is also likely to be large.

Because there are both elements, it is dangerous to decide that “it will continue to rise” just by looking at yesterday’s strength.

Checking the position of the stock price: The surge from the beginning of the year and recent waves

Let’s look back at the stock price with a slightly longer view. The opening price of 2026 (January 5) was 6,726 yen. Since it rose to yesterday’s closing price of 17,280 yen, it is calculated to have become about 2.6 times higher since the beginning of the year.

This year’s high was 20,495 yen on May 14, and it is currently about 16% below that. In other words, it is in a position where “there is still distance to this year’s highest price.”

Organizing the recent movements, it is like this:

• September 8: Hits a high of 16,715 yen
• September 14: Sharp adjustment to a low of 12,885 yen (about 23% decline from the high)
• September 28: Closing price 14,695 yen
• October 1: Closing price 15,895 yen (+6.07%)
• October 2: Closing price 17,280 yen (+8.71%)

September was a month with a very large price range from high to low. I want to keep firmly in mind that it is a stock with volatile price movements.

The Nihon Keizai Shimbun has reported many times since entering 2026 that Resonac hit its highest price in about 36 years. It is often talked about as a “stock that has escaped from long-term stagnation” in the sense that the stock price is at a level since around 1989 to 1990. However, because of that, short-term price movements tend to be large.

Points to be careful about: Sense of being expensive and reaction after a surge

I have looked mainly at good materials so far, but there are also points I want to check calmly.

① Valuation is by no means cheap

Based on yesterday’s closing price, the expected PER is 29.1x, and the PBR is about 4.7x. The dividend yield is quite low at 0.37%. It is a stock price level bought on expectations for growth, and the room for decline when expectations are betrayed is also large.

② Reaction after rising more than 15% in 3 days

Stocks that have surged in the short term are prone to profit-taking selling. On bulletin boards, voices were also seen saying, “The rise of these 3 days is amazing, I took some profits.” It is hard to notice while the rise continues, but in a phase where sellers increase, price movements are prone to reverse rotation.

③ The increase in shareholding ratio is a “story that has already happened”

As mentioned above, the buying increase was as of September 25. Yesterday’s material is a “re-evaluation through disclosure” rather than a “new change” in supply and demand. I want to be careful about the exhaustion of materials.

④ Swayed by semiconductor market conditions

Even though AI demand is a tailwind, there are waves in the semiconductor industry market. Although there are many positive elements such as the recovery trend of the memory market, there is also a possibility that demand will temporarily fall in the form of a slowdown in capital investment or inventory adjustments by customers.

⑤ Split in evaluation

While there is a bullish view that sets the target price at 22,800 yen, the average prediction of individual investors is lower than yesterday’s stock price. The fact that views are split means that price movements are prone to be that much larger.

Points to watch going forward

There are four key points to keep in mind when looking at Resonac’s stock price moving forward. 1. The next earnings report (Q3 of the fiscal year ending December 2026). The biggest focus will be on how much the sales and profit margins of the semiconductor and electronic materials business have grown. We want to confirm whether price hikes for back-end materials have taken hold and whether sales of copper-clad laminates for AI are increasing. 2. Follow-up reports on large shareholdings. Whether major investors like Capital Research will further increase or decrease their holdings. New change reports will be a clue to gauging the direction of supply and demand. 3. Trends at Kurashiki Chemical. The stock price and dividend policy of the new company after the separation will indirectly affect the valuation of Resonac itself. It is important to see if the results of the separation become visible in the numbers. 4. Distance from the year-to-date high of 20,495 yen and price movement at the start of the week. The distance from Friday’s closing price is about 16%. If it exceeds this, it will enter historical high territory again. The next trading session is Monday, October 5th, and since it rose significantly over three days, whether it can absorb profit-taking and maintain levels around 17,000 yen or in the 16,000 yen range will likely be a barometer of short-term strength.

Summary

Resonac’s 8.71% gain on October 2nd can be summarized as being caused by the following overlapping factors: • It was revealed that the holding ratio of US-based Capital Research and others rose from 11.62% to 12.40% (the direct trigger) • The spin-off and listing of the petrochemical business made its profile as a semiconductor materials company clearer • Securities companies successively raised their target stock prices • The selection of a supplier for the green ammonia demonstration served as additional material • Funds flowed into stocks with strong individual catalysts while the Nikkei Average fell. On the other hand, there are still points to view calmly, such as the expectation-driven level of a forward P/E ratio of about 29x, the sharp rise of over 15% in three days, and the risk of “selling on the news” regarding the catalysts. Resonac is a “company that is being reborn as a semiconductor materials firm after years of stagnation.” Whether the market continues to believe in that story depends on the earnings figures that will be released from here on out. Yesterday’s stock price can be said to be a day that reflected the magnitude of those expectations.