Days after a world-first in diamond semiconductor switching, the same Japanese startup hit another milestone: proving its diamond chip can actually convert power inside a real circuit. The "ultimate semiconductor" is climbing toward practical use one step at a time.

From Device to Circuit: Diamond MOSFET Levels Up

On March 18, 2026, Tokyo-based startup Power Diamond Systems (PDS) announced a new breakthrough. The company fabricated an asynchronous rectification step-down DC-DC converter using a diamond MOSFET and successfully demonstrated continuous switching operation with actual power conversion, a world first for diamond-based devices.

Just six days earlier, on March 12, the same company had achieved the world's first 200V/1A switching operation with a diamond MOSFET. That device used a field-plate structure to suppress electric-field concentration at the gate edge, combining a 550V breakdown voltage with 0.8A of drain current in a single element; the paper was accepted by Applied Physics Express on February 24, 2026. What it proved was raw capability: how much voltage and current the transistor could handle on its own.

This time, PDS went further, embedding that diamond MOSFET into an actual power conversion circuit to see whether it could convert electrical power. Output voltage tracked the duty cycle accurately, confirming stable converter operation. High-speed switching in diamond MOSFETs had already been shown; continuous switching, the operating mode real power electronics equipment demands, had not been adequately verified. That gap is now closed.

Why "Working in a Circuit" Is a Big Deal

Semiconductor device development follows a progression. First, researchers study the material's properties. Then they build a device and measure its characteristics (static testing). Next comes switching tests to evaluate how fast it turns on and off and how much energy is lost (dynamic testing). Beyond that lies the crucial step of integrating the device into an actual power conversion circuit.

A DC-DC converter is a device that transforms direct current from one voltage level to another. They're found in virtually every modern electronic device, from smartphone chargers to EV powertrains. The type PDS built, an asynchronous rectification step-down converter, is one of the most fundamental topologies there is: take a higher voltage, deliver a lower one.

If the previous switching result was a fitness test for an athlete, the DC-DC converter demonstration is closer to scoring in an actual game. The device did work inside a circuit, not on a probe station.

Why Diamond Is Called the "Ultimate" Semiconductor

Diamond's appeal as a semiconductor material comes from physical properties that dramatically surpass today's leading materials, silicon carbide (SiC) and gallium nitride (GaN).

Its dielectric breakdown strength is roughly 30 times that of silicon, meaning diamond devices can handle far higher voltages while remaining physically compact. Its thermal conductivity is the highest of any known material, offering a fundamental solution to the heat management challenges that plague power semiconductors. And its bandgap of approximately 5.5 eV, against 3.2 to 3.4 eV for SiC and GaN, enables stable operation at extreme temperatures and in radiation-heavy environments.

In theory, diamond could deliver conversion efficiency and miniaturization several steps beyond SiC and GaN. The engineering problem is achieving high breakdown voltage and low on-resistance at the same time.

Rapid-Fire Milestones: PDS's Development Timeline

PDS was founded in August 2022 as a Waseda University spinoff, built on more than two decades of research by Hiroshi Kawarada, professor emeritus at Waseda's Faculty of Science and Engineering, and his colleagues. In three and a half years, the results have stacked up:

  • 2023: Developed a normally-off diamond MOSFET using a silicon-oxide termination structure
  • December 2025: Demonstrated live diamond MOSFET operation at SEMICON Japan 2025
  • March 12, 2026: Achieved world's first 200V/1A switching with a 550V-rated, 0.8A diamond MOSFET
  • March 18, 2026: Demonstrated world's first DC-DC converter power conversion using a diamond MOSFET ← this article
  • April 2026: Developed a monolithic bidirectional diamond switch, raising breakdown voltage while cutting on-resistance to under a tenth of conventional bulk-conduction designs

Going forward, PDS plans further device characterization plus circuit design and system evaluation aimed at specific applications. The company is also working with JAXA, gathering baseline data on power MOSFETs for spacecraft. CEO Tatsuya Fujishima targets practical deployment in the 2030s and frames 2026 through 2030 as five years of laying groundwork, while seeking partners in applications such as EVs and base stations.

Japan's Diamond Semiconductor Ecosystem in Motion

PDS's achievement doesn't exist in isolation. Japan is advancing diamond semiconductor technology on multiple fronts simultaneously.

Honda and AIST (National Institute of Advanced Industrial Science and Technology) demonstrated ampere-class high-speed switching with a p-type diamond MOSFET in 2025, targeting future mobility applications. NIMS (National Institute for Materials Science) developed the world's first n-type diamond MOSFET in 2024. AIST and EDP Corporation have also developed large-area diamond/silicon composite wafer technology.

On the industrial side, Okuma Diamond Device in Fukushima Prefecture is building the world's first diamond semiconductor mass-production factory, set to begin operations during fiscal year 2026. On substrates, Orbray has established production technology for 3-inch single-crystal diamond in partnership with the UK's Element Six, with 2-inch wafer mass production in its final preparation stage.

For background on diamond semiconductor fundamentals, how it compares with SiC and GaN, and why Japan leads this field, see our earlier piece on the 200V/1A switching result.

Diamond semiconductors in Japan are steadily transitioning from "research topic" to "industrial reality." In your country, are diamond semiconductors on anyone's radar? What expectations do you have for next-generation power semiconductor materials? We'd love to hear your perspective.

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