Ishii Osamu was born on October 11, 1929, and graduated from Department of Electrical Engineering, School of Engineering of Keio Gijyuku University in March 1952. Right after his graduation, Ishii joined Electrical Communication Laboratory on Ministry of Electrical Communications, and was assigned to do research on magnetic material at Hichijyo Yuzo's laboratory of Materials and Components Development Division. Seven years later, he moved to the Electrotechnical Laboratory, MITI, suggested by Takahashi Shigeru, one of his seniors in alumni of the School of Engineering of Keio University.

It was just when people were fussing over Esaki diodes, and when Takahashi returned from abroad and launched a plan of building a very fast computer ETL Mark VI. While Takahashi and Ishii were discussing, over a blackboard, a high-speed scratch pad memory to be used for Mark VI, they came upon an idea on a high-speed memory component consisting of an Esaki diode, a resistor and a normal diode. Ishii materialized this idea in the high-speed memory unit of the ETL Mark VI, but it was not further developed, because Esaki diode that was the essential part of this memory turned out a failure as commercial product.

In the academic year of 1963-1964, Ishii visited the University of California, Los Angels (UCLA) and joined the Jerry Estrin's group to work on the project of a variable structure computer. After returning from UCLA, Ishii participated in MITI's large-scale projects, "Ultra-high Performance Computer" and "Pattern Information Processing System." In September 1966, Ishii was awarded a Degree of Ph.D., by Keio University, for his thesis entitled, "Research on High-speed Storage Unit using Esaki diodes." Though Ishii was appointed Head of Software Division of the ETL in November 1972, his own interests on research had been always around memory unit.

Ishii left the ETL in March 1983, and was appointed a professor of Japan Institute of Technology on April 1, 1983. At the same time, he was a Visiting Professor of the School of Science and Engineering of Keio University. He was Chairman of the National Committee, for standardizing flexible magnetic media, of the Information Processing Society of Japan, and Chairman of the IEEE Tokyo Chapter. Ishii was a good writer, and published many essays on computer technologies, particularly on memories. Some of them were edited and compiled as books such as "Logic and Memory," "Memory and Device" and "VLSI and Information Processing."

Ishii died on August 28, 1988.