The Day CPUs Rallied Again: From the US Session to Korea's Substrate Names

Tue, 22 Sep 2026 01:35:00 +0900

In the US session on September 21, CPU names suddenly became market leaders. ARM rose 16.0%, Intel 13.1%, AMD 9.2%.

The surface trigger was Meta’s AI agent app Muse hitting number one on the app store. The market quickly translated one app’s success into more agentic AI usage, more inference calls, and more server CPU demand.

If that translation is right, where do you look in Korea? Higher CPU revenue pulls package substrate demand with it. But there is a gap between today’s price reaction and actual orders. This piece is an attempt to separate that gap with numbers.

Facts: only CPUs were strong

Line up the September 21 moves and the market’s intent shows.

Segment	Name	Move
CPU IP	ARM	+16.0%
CPU	Intel	+13.1%
CPU	AMD	+9.2%
Server OEM	Dell	+1.4%
Networking	Arista Networks	+1.6%
Power & cooling	Vertiv	+1.6%
ASIC & networking	Broadcom	+0.6%
Server OEM	HPE	+0.6%

24/7 Wall St. noted there were no new product announcements from the companies themselves, and that the Muse reaction triggered a CPU demand repricing. AI agents do not run on accelerators alone. Dispatching requests, moving data, and coordinating tool calls all require CPUs.

Server, networking and power infrastructure names, by contrast, sat in a 0-1% range. This was not a session where CPU demand was confirmed as broad orders across datacenter equipment.

Interpretation: the bottleneck got repriced first

In training-centric AI investing, GPUs and HBM ran short first. As inference grows and agents run longer chains of tasks, the system bottleneck shifts. The share of CPUs, memory and networking that coordinate work around the GPU gets larger.

This rally is an early pricing of that change. There is no evidence yet that Muse created actual server CPU orders. An app ranking is a usage signal, and a 9-16% price move is what happens when the market converts that signal into long-term demand.

So the next indicators to confirm are not stock prices.

Server CPU orders and shipments at cloud operators
ARM server share and datacenter revenue at Intel and AMD
Order backlogs at server OEMs
Utilization, pricing and lead times at ABF substrate makers

For the CPU rally to continue, the breadth needs to widen to server OEMs like Dell and HPE and to substrate orders.

The link from CPUs to ABF

High-performance CPUs and AI accelerators sit on FC-BGA package substrates. ABF insulating film goes in to build the fine circuitry. As chip area and I/O counts grow, substrates go larger and higher-layer.

The logical chain looks like this:

CPU shipments up → FC-BGA content up → ABF substrate area and layer counts up → utilization and pricing improve

One caveat. High-spec ABF capacity is claimed by AI accelerators first. Substrates for general server CPUs are closer to commodity. A CPU stock rally alone does not raise earnings estimates at Korean ABF makers. Server shipment recovery and an actual substrate mix improvement need to show together.

The overseas comparison group is Ibiden and Shinko in Japan, and Unimicron, Nan Ya PCB and Kinsus in Taiwan. When looking at Korean names, check these peers’ utilization and pricing direction in parallel.

Daeduck Electronics: the most direct ABF idea

Daeduck Electronics (353200) is the Korean name where this CPU logic connects most directly.

Confirmed facts

September 21 close: ₩101,900
Down 49% from the 52-week high of ₩198,000
One-year return: +404%
ABF lines effectively at full utilization
Mass production started on large-area ABF for AI networking
Initial yield around 70%, above the previously expected 50%
Mass production for another networking customer scheduled for late September
Advance payments received from some customers
Meritz Securities target price: ₩180,000

On price alone the stock has halved from its high, but over one year it is still a five-bagger. That is why a big drawdown and cheap valuation are not the same word.

The investment logic is being confirmed first in large-area ABF for AI networking, not CPUs. A 70% initial yield signals lower mass-production risk than feared. Advance payments are evidence that customers want to lock in capacity.

For the CPU rally to become additional fuel, server CPU ABF orders need to stack on top of the existing AI networking volume. The numbers to watch: the timing of new customer ramps, the ABF revenue mix, quarterly yields, and the conversion of advance payments into revenue.

Flow: foreigners bought, institutions sold

Cumulative flow over the last 20 sessions: foreigners +1,861,467 shares, institutions -2,857,483 shares, retail +981,721 shares. Since late August, foreign buying against institutional selling has been the clear pattern.

Foreign ownership rose from 13.66% on August 18 to 18.32% on September 21, up 3.48 percentage points over 20 sessions. Foreigners absorbed the institutional supply, but institutional selling was too large to turn the price trend.

On August 21 the stock dropped 8.02% to close at ₩104,300 on volume of 668,559 shares. Some articles blamed joint selling by foreigners and institutions, but the confirmed KRX figures say otherwise. Institutions net sold 257,888 shares while foreigners net bought 188,732. Short selling that day was 4.03% of volume, nothing unusual. The direct flow pressure behind the drop points to institutions.

Short-selling pressure has eased. Weekly short volume ratio fell from 11.80% in the week of July 13 to 1.86% in the week of September 14. Net short balance also shrank from 90,060 shares on August 20 to 19,950 on September 17.

That said, September 21 brought joint net selling: foreigners -57,044 shares, institutions -64,646. One day does not make a trend, but it is the point to check whether the rise in foreign ownership is breaking.

Simmtech: a SoCAMM2 memory chain, not CPU

Simmtech (222800) is in the same substrate industry but connects through a different link. The current catalyst is Nvidia’s SoCAMM2 rather than CPU ABF.

Confirmed facts

Price ₩125,700, +49% over the past month
The only vendor supplying both modules and substrates to all three memory makers
SoCAMM2 revenue outlook: ₩151.8B this year → ₩321.0B next year, +111.5%
Daishin Securities target price: ₩170,000
Foreign net buying for five straight sessions

SoCAMM2 is the low-power memory module for AI servers. Simmtech supplies both the module and the LPDDR5 substrate, capturing rising per-server content in two product lines.

But a stock up 49% in a month likely already reflects much of the doubling revenue forecast for next year. What is needed now is not a new theme but quarterly revenue recognition and margins. The CPU rally is an indirect tailwind for Simmtech; the variable that moves earnings estimates is SoCAMM2 shipments.

Korea Circuit: the cheapest looking, with the most to confirm

Korea Circuit (007810) trades at ₩50,100, down 66% from its 52-week high of ₩148,300. It has fallen the most, but its earnings and flow are also the weakest.

Confirmed facts

Q2 operating profit ₩19.3B, 41% below consensus
Meritz Securities cut its target from ₩170,000 to ₩90,000
Memory module capacity expansion effect delayed from Q3 to Q4
SoCAMM revenue outlook: ₩62.0B this year → ₩176.3B next year
ABF price increase secured
Foreign and institutional net selling continues

The Q4 turnaround conditions are clear. The delayed expansion volume must show up as actual revenue, domestic customer SoCAMM shipments must begin, and the ABF price increase must land in earnings.

A large drawdown alone is not enough reason to buy ahead, given how big the Q2 miss was. If any of the three conditions slips again, even the estimates after the target cut can wobble. Conversely, if Q4 revenue and flow turn together, this name has the largest price elasticity of the three.

What you are buying in each name

Name	Main exposure	Confirmed now	Still needed
Daeduck Electronics	AI networking ABF, server CPU optionality	Full utilization, large-area mass production, 70% yield	New customer revenue conversion, server CPU orders, flow turn
Simmtech	SoCAMM2, memory modules and substrates	Revenue doubling forecast, consecutive foreign buying	Quarterly shipments and margins, digesting valuation after the rally
Korea Circuit	SoCAMM + ABF turnaround	Price increase, Q4 expansion effect scheduled	Delay resolution, earnings confirmation, foreign and institutional buying

I read Daeduck as the best quality of evidence today, Simmtech as the best earnings visibility, and Korea Circuit as the largest reversal asymmetry. They get grouped as substrate names, but the investment clocks and failure conditions differ.

Conclusion

The September 21 US session was not a broad AI infrastructure rally; it was a session where CPUs got repriced. Muse’s success signaled that agentic AI can grow not only GPU usage but also CPU coordination and inference load.

Mapping this to Korean substrate names requires one more step of verification: whether the CPU stock move spreads into server shipments and ABF orders, and whether high-spec capacity can take CPU volume on top of AI accelerators.

Daeduck is closest to that link. Simmtech already has a separate earnings axis in SoCAMM2. Korea Circuit needs its Q4 schedule and a flow turn confirmed first.

Today’s CPU surge is the starting point of an investment idea. To become a reason to buy, the path from app rankings to server orders, and from server orders to substrate utilization and earnings, needs to show up in quarterly numbers.

Sources

This piece is an investment idea based on public sources and is not a recommendation to buy or sell any security.

Semiconductor Substrate on Korea Invest Insights

The Day CPUs Rallied Again: From the US Session to Korea's Substrate Names

Facts: only CPUs were strong

Interpretation: the bottleneck got repriced first

The link from CPUs to ABF

Daeduck Electronics: the most direct ABF idea

Flow: foreigners bought, institutions sold

Simmtech: a SoCAMM2 memory chain, not CPU

Korea Circuit: the cheapest looking, with the most to confirm

What you are buying in each name

Conclusion

Sources