Resonac announced on September 15, 2026 that it had succeeded in growing and processing 300mm (12-inch) SiC single crystals, a next-generation electronics material. By the company's own survey of public information as of August 2026, this ranks among the largest SiC substrate sizes currently under development anywhere.
What matters is that this is not a production announcement. SiC substrate diameters are only now beginning to move from 150mm (6-inch) to 200mm (8-inch). In the middle of that transition, Resonac grew a crystal at a still larger dimension and carried it through processing.
Where the company actually stands: 6-inch mainstay, 8-inch shipping
Miss this and you misread the announcement. The volume market still runs on 150mm, and that is where Resonac's supply is concentrated. It has already begun shipping 200mm epitaxial wafers, but the centre of gravity for volume production has not moved there.
So 300mm should be read not as an option you can build into a supply plan, but as a technical marker of how far the diameter roadmap can reach. We have covered the readiness of 8-inch substrate supply and the Mitsubishi Electric–Coherent move on 8-inch substrates; the industry as a whole is still in the 8-inch ramp phase.
Seen that way, the significance of 300mm is not when you can buy it but that the ceiling on diameter is still somewhere further out. Since substrate cost is felt per die rather than per wafer, where that ceiling sits feeds directly into medium-term price expectations.
Japan's NEDO Green Innovation Fund sits behind the work
The result incorporates R&D carried out under the Green Innovation (GI) Fund established within NEDO, Japan's New Energy and Industrial Technology Development Organization, to support the country's 2050 carbon neutrality goal — specifically its project on SiC wafer technology for next-generation green power semiconductors.
For procurement, the fact that large-diameter SiC substrate development is proceeding under public funding is worth reading closely. Which governments are funding which stage of the technology tends to show up years later in who can supply larger diameters first. SiC substrates are an area where crystal growth yield governs the return on investment, so development speed is not set by a single company's decisions alone.
The applications are moving beyond power devices
The other detail not to overlook is how Resonac describes the end uses.
Power devices
The traditional core use. Lower conversion loss and less heat generation than silicon-based devices, with adoption expanding mainly in EVs and renewable energy.
AI server and HPC thermal management
High thermal conductivity makes it a candidate for heat-spreader substrates and advanced packaging substrates in semiconductors used for AI servers and HPC.
Optical uses
A high refractive index puts applications such as AR smart glasses on the candidate list.
SiC demand has conventionally been discussed across three power-conversion segments: EVs, renewable energy, and data centre power. Add thermal management material for AI servers as a separate stream, and the primary driver of demand could change.
Thermal applications call for different characteristics than power conversion. What matters is thermal conductivity and substrate flatness rather than the defect density required for a working device. If that use case ramps, crystal grades hard to use for power devices gain an outlet, and the economics of crystal growth itself shift. That in turn feeds back into investment decisions on larger diameters.
What procurement and design should watch now
300mm is not a procurement option for the foreseeable future. Two things still make it worth tracking.
First, as a reference point when planning the 8-inch transition. If the technical ceiling on diameter lies further out still, 8-inch is a waypoint rather than a destination. Long-term supply agreements need a view on how diameter generations turn over.
Second, as a risk that the demand mix for SiC substrates changes. If thermal and packaging use in AI servers takes off in earnest, it could compete with power device supply for the same substrates. Looking at SiC substrate price trends with EV demand as the only variable will mislead.
What is confirmed at this point is two facts: that Resonac succeeded in growing and processing 300mm, and that its production position today is 150mm as mainstay with 200mm shipments started. No timeline for volume production or supply plans was given in this announcement.