Masahito (Masa) Yokoyama, a founding attorney of Xsensus, has more than 20 years of comprehensive legal experience including: patent preparation and prosecution; patent portfolio development and management; drafting claims to cover industry standards; opinions of counsel; due diligence; enforcement counseling; licensing; and pre-litigation counseling.

Early in his career, Mr. Yokoyama served as a patent attorney in the intellectual property division of Hitachi, Ltd., as well as Sony Corporation, where he focused on patent portfolio development and management, pre-litigation analysis, patent litigation, patent enforcement and licensing.

Before joining Xsensus, Mr. Yokoyama served as a partner of a D.C. area intellectual property law firm. Leveraging the rare combination of experience both in Japan and U.S., Mr. Yokoyama has supported world leading companies in various IP matters including strategically developing patent portfolios to protect their business. Mr. Yokoyama is the author of many articles and often gives lectures to companies and IP associations in Japan.

Mr. Yokoyama is a native of Japan and is particularly skilled at providing clients with practical advice on obtaining quality patents in a cost-effective way through legal and technical analysis.

Mr. Yokoyama’s work focused on industries such as:

  • Consumer electronics
  • Computer software
  • Information technology
  • Communication/broadcasting technologies
  • Medical devices
  • Factory/building automation and control system
  • Measurement technologies
  • Display technologies
  • Data storage technologies
  • Imaging technologies
  • Auto technologies
  • Semiconductor devices
  • Optics
  • Life sciences
  • Pharmaceuticals
  • Genetic Engineering
  • Materials
  • Polymers
  • Biomaterials
  • Plastics
  • Catalysts
  • Ceramics
  • Crystals

横山 昌史はXsensusの創立メンバーであり、特許出願・権利化、特許ポートフォリオマネジメント、技術標準関連特許の権利化、鑑定、特許クリアランス(Freedom to Operate)、権利行使時のカウンセリング、ライセンス、訴訟前のカウンセリングを含む幅広い知財分野において20年以上の経験を有します。


横山氏はXsensus創立の前はワシントンD.C.エリアのIP系法律事務所のパートナー弁護士として勤務しておりました。横山氏はワシントンD.C. 弁護士および弁理士(米国および日本)であり、その非常に稀な日本企業知財部と米国法律事務所、両者での経験を活かし、多くの日本企業に米国特許ポートフォリオ構築のサポート、特許係争のサポート、米国進出にあたっての特許リスク評価を含む、幅広い知財に関するアドバイスを行ってきました。また、横山氏は米国特許に関する数多くの執筆とセミナーを日本で行っております。



  • University of Pennsylvania Law School (LL.M.)
  • Chuo University (LL.B.)
  • University of Tokyo (M.E.)
  • University of Tokyo (B.E.)

Bar Admissions

  • District of Columbia
  • Japan Patent Office
  • Tokyo and Osaka District Courts and IP High Courts in specified infringement litigation
  • Registered to practice before the U.S. Patent and Trademark Office


  • Named ‘IP Star’ by Managing Intellectual Property’s IP Handbook (2023). MIP’s listing of the country’s leading intellectual property attorneys is based on surveys and interviews with peers and in-house counsel.
  • Intellectual Asset Management (IAM) Patent 1000: The World’s Leading Patent Practitioners, named to its list of the top 1000 patent attorneys in the world and is a “Recommended” patent attorney in the Washington, D.C. Metro Area for his patent prosecution expertise (2021-2023)

Professional Affiliations

  • District of Columbia Bar
  • Japan Patent Attorney Association

Prior Affiliations

  • Oblon
  • Sony
  • Hitachi