Seimiya Hiroshi was born on August 6, 1908, and graduated from Department of Electrical Engineering, School of Engineering of Tokyo Imperial University in March 1932. Immediately after the graduation, he joined the Electrotechnical Laboratory (ETL) of Ministry of Communications, where he was assigned to do research on optical communication, novel electron tubes such as magnetron and velocity modulation tube, etc. Seimiya together with Seki Takeo and Nijo Sukemoto established Jindai Annex of the ETL in 1944. Jindai Annex became ETL's Seventh Research Division in January 1945 that was renamed Electron Tube Research in May 1945. In August 1948, communication-related research group including the Electron Tube Research Division was separated from the ETL when Seimiya was the head of that Division.

In 1949, when Electrical Communication Laboratories (ECL), Ministry of Electrical Communications was established, major part of it being the group separated from the ETL, Seimiya was appointed the head of Parts and Materials Development Division of the ECL (In 1952, ECL became a part of NTT). In January 1955, Seimiya resigned from NTT as its Director of the Board, and joined Fujitsu, where he was appointed a Director of the Board in November 1955. After serving as a Managing Director and Vice President, Seimiya was made President of Fujitsu in April 1974. On April 27,1976, he died as the Chairman of the Board to which he was appointed in March 1976.

Ministry of International Trade and Industry (MITI) had committed to lift, one by one from 1971, various barriers against importation of computer systems and equipment for protecting Japanese computer makers. As measures collateral to the removal of these barriers, MITI decided to give a subsidy to Japanese computer makers to enable them to be competitive in the international marketplace. MITI wanted the six makers to form themselves into two or three groups, each group to develop a series of new computers, and started negotiations with them in September 1971. Seimiya as the Vice President of Fujitsu and Kubo Toshihiko as the Vice President of Hitachi quickly agreed to form the group prior to others. It is well known that friendship between them through their Alma Mater helped create this group so quickly.

Seimiya being a good opponent of Ikeda Toshio in 'go', helped Ikeda to fully utilize his genius as the Director responsible for computer business. Seimiya usually left detailed decisions for younger people, but made a brave decision to move in on the matter, when Amdahl got into a bad shape and Fujitsu Management was divided as to further supporting Amdahl.

Because of his illness, Seimiya did not long remain in the position of President, but, while he was there, a negotiation was going on for Fujitsu to provide Siemens with mainframe computer technologies. Seimiya being extremely enthusiastic in materializing this technical aid agreement, he wrote a letter himself to Siemens in bed. (The agreement was materialized in April 1978, 2 years later than he died).