The company was established in Seinäjoki, Central Finland in 1975 under the name of Semtu Oy/Seinäjoen tehdas. Following a merger in 1995, the company was renamed SEMKO OY Semtun konepaja. Finally, in 2003, the name was changed to Semko Oy.

Semko Oy operates in the building industry, the main products being cast-in details, various fixings, concrete handling equipment and lightweight steel structures. The company also manufactures highway railings and traffic portals. The production is carried out in accordance with the ISO 9002 standard. Most of the production consists of welded products with a considerable percentage of the items being made on automated production lines.

Semko Oy´s products and processes are certified by the Finnish Concrete Association. Semko Oy´s operations are monitored by Inspecta Oy of Finland.

The company´s 2007 turnover was about 7 million € and the number of staff 30 persons.