It was founded in 1939 by the merger of Nihon Electrical Industries and Showa Fertilizers, both established by a Japanese entrepreneur Nobuteru Mori.

The company is divided in five business sectors: petrochemicals (olefins, organic chemicals, plastic products), aluminum (aluminum cans, sheets, ingots, foils), electronics (semiconductors, ceramic materials, hard disk drive platters), chemicals (industrial gases, ammonia, agrochemicals), and inorganic materials (ceramics, graphite electrodes).

The company has vast overseas operations and a joint venture with Netherlands-based Montell and Nippon Petrochemicals to make and market polypropylenes.

As the semiconductor industry shifted to other Asian locations, SDK established overseas specialty gases production sites in Shanghai and Singapore.

[6] The Electronics Sector includes compound semiconductors, rare-earth magnetic alloys, solid aluminum capacitors, and hard disks.

In September 2008 SDK announced a consolidation their hard disk (HD) media operations by establishing a joint venture with Hoya corporation in January 2009.

However, this joint venture ended in March 2009 due to the rapid deterioration of the global economy in the Hard Disk Sector.

The company is known for causing the second outbreak of Minamata disease (a type of severe mercury poisoning) in Kanose, currently part of Aga-machi, Niigata Prefecture, through the release of organomercury compounds into the Agano River.

[8]: 327–328  Multiple epidemiological studies[7][9][10] traced an outbreak of eosinophilia-myalgia syndrome (EMS) to L-tryptophan supplied by Showa Denko, which resulted in 37 deaths.