TEAM

Shaping the world with diamond semiconductors.
Experts from diverse fields are coming together at Ookuma Diamond Device.

Naohisa Hoshikawa
CEO
Naohisa Hoshikawa
Hoshikawa Naohisa

Founded his first company while enrolled in the Graduate School of Accounting at Hokkaido University, achieving six consecutive profitable fiscal years before exiting through a successful business sale. Joined the field of diamond semiconductor research in 2016 and founded the company in 2022. Well-versed in both management and technology, he has secured over 2 billion yen in total research funding. Recognized as the first student to receive business financing from The Hokkaido Bank. Selected in the Forbes Japan Startup Encyclopedia in 2025.

Junichi Kaneko
Director
Junichi Kaneko
Kaneko Junichi

Graduated from Nagoya University and earned his Ph.D. in Engineering from the University of Tokyo Graduate School. After working at the Japan Atomic Energy Research Institute, he joined the Graduate School of Hokkaido University as an Associate Professor. Earned an MBA from Otaru University of Commerce. From 2017 to 2023, served as Assistant to the President and Deputy Director of the Organization for Promotion of University-Community and Industry Collaboration. Successfully commercialized diamond detectors and GPS scintillators. Currently advancing the development of diamond semiconductor devices in collaboration Hitoshi Umezawa and others.

Hitoshi Umezawa
Director / CTO
Hitoshi Umezawa
Umezawa Hitoshi

Received his Ph.D. in Engineering from the Graduate School of Waseda University in 2002. Since 2005, he has been affiliated with the National Institute of Advanced Industrial Science and Technology (AIST). Since 1997, he has been engaged in research on wide-bandgap semiconductors, primarily focusing on diamonds. His areas of expertise include semiconductor engineering, materials engineering, power devices, and RF devices.

Yuhei Nagai
CFO
Yuhei Nagai
Nagai Yuhei

Graduated from the Graduate School of Engineering, Hokkaido University. Began his career at Sojitz Corporation, where he was involved in cross-border mergers, acquisitions, and related operations. At Terra Drone Corporation, he led the acquisition, post-merger integration, and subsequent divestiture of a local company as regional head of the CIS area. Upon returning to Japan, he served as CFO and led a successful Series A fundraising round of over 1.5 billion yen. He has been involved with Ookuma Diamond Device since before its founding and officially joined as CFO in June 2023.

Takahiro Yamaguchi
Director of Technology Strategy Department
Takahiro Yamaguchi
Yamaguchi Takahiro

While enrolled in the Graduate School of Engineering at Hokkaido University, he conducted intensive research on diamond semiconductor devices under the guidance of Dr. Umezawa and Dr. Kaneko, leading to a key technological breakthrough that became the foundation for the company’s establishment. After graduation, he worked as a strategy consultant at McKinsey & Company, but his passion for research remained strong. He joined this company as its first full-time employee at the time of its founding. He currently serves as director of the Technology Strategy Department, driving both the development and practical application of core technologies.

Hiroyuki Kawashima
Director
of Process Development
Hiroyuki Kawashima
Kawashima Hiroyuki

After working with materials such as GaN, he spent over a decade conducting research on diamond at institutions including the National Institute of Advanced Industrial Science and Technology (AIST) and Kyoto University. Since then, he has collaborated extensively with Director Hitoshi Umezawa on the research and development of various diamond semiconductor devices. A true all-rounder, he is proficient in design, synthesis, processing, and measurement. He earned his Ph.D. in Engineering from the Graduate School of the University of Tsukuba while engaged in diamond research.

ADVISORS

Takehiro Kamigama
Takehiro Kamigama
Kamigama Takehiro
Profile
  • 1981 : Joined Tokyo Denki Kagaku Kogyo K.K. (now TDK Corporation)
  • 2006 : Appointed President and Representative Director, TDK Corporation
  • 2016 : Appointed Chairman and Representative Director, TDK Corporation
  • 2017 : Appointed Outside Director, OMRON Corporation (current)
  • 2017 : Appointed Outside Director, SoftBank Corp. (current)
  • 2021 : Appointed Outside Director, KOKUYO Co., Ltd. (current)
  • 2021 : Appointed President and CEO, Gama Expert Inc. (current)
Toshiyuki Umehara
Toshiyuki Umehara
Umehara Toshiyuki
Profile
  • 1984 : Joined Nitto Denko Corporation
  • 2010 : Appointed Executive Officer, Nitto Denko Corporation
  • 2019 : Appointed Representative Director and Executive Vice President, CTO and CIO, Nitto Denko Corporation
  • 2020 : Appointed Executive Trustee (part-time), Hokkaido University / Visiting Professor, Keio University
  • 2021 : Appointed Outside Director, Fuji Oil Group Inc. (current)
  • 2022 : Appointed Outside Director, ShinMaywa Industries, Ltd. and Daiichi Kigenso Kagaku Kogyo Co., Ltd. (current)
  • 2023 : Appointed President and CEO, JCCL Inc. (current)
Tatsuyuki Maekawa
Tatsuyuki Maekawa
Maekawa Tatsuyuki
Doctor of Engineering, Professional Engineer (Nuclear and Radiation Division)
Profile
  • 1984 : Joined NAIG (Nippon Atomic Industry Group)
  • 2005 : Appointed General Manager, Measurement and Inspection Technology Development Department, Nuclear Technology Research Center, Toshiba Corporation
  • 2010 : Appointed General Manager, Reactor Instrumentation and Control Design Department, Isogo Engineering Center, Toshiba Corporation
  • 2014 : Appointed Director, Isogo Engineering Center, Toshiba Corporation
  • 2015 : Appointed Senior Managing Director and CTE, Toshiba Energy Systems & Solutions Corporation – Radiation Technology & Service
  • 2022 : Founded TM RAMS Consulting, Engineering Office (current)