The company was created with the aim of designing and building industrial facilities. During its early years, it shapes its innovative and pioneering vocation, specialising in the development and commissioning of the national power transmission network, including high-voltage electrical power lines and substations.

SEMI presented the “Project for the construction of a National Electricity Grid in Spain”, which involved the creation of a Body, the precursor to the current Red Eléctrica de España (REE).

SEMI has been operating in the railway sector since 1929. The company started its activities with the electrification of the Madrid-Ávila-Segovia line, the first electrification activity to be carried out by a Spanish company in Spain.

This project was begun for the Compañía de los Caminos de Hierro del Norte de España, which was later integrated into RENFE.

As the works were interrupted by the Spanish Civil War, the electrification could not be concluded until 1946, when RENFE had already taken over (established in 1941).

SEMI designed and built the Ponferrada-Valladolid line for Endesa. It was the first 220 kV voltage line in Spain.

The desire to progress and to face new challenges helped the company establish itself in the telecommunications field. Since then, SEMI has developed a large number of activities in all operations related to the design and construction of communications infrastructures: television, radio, mobile telephone, and GSM-R repeaters; radar and maritime rescue stations; fibre optic networks, real-time data weather stations, etc.

SEMI built the aerial field for the Noblejas Shortwave Broadcasting Station, from where the Radio Nacional de España (RNE) broadcasts are to be transmitted to Eastern Europe, the Middle East, Australia, North Africa, Equatorial Africa and America.

In the 70s, SEMI designed and built the first line transformation carried out in Spain for a duplex 220 kV line to a triplex 400 kV line, Madrid-La Mudarra.

Held in Spain with “Naranjito” as mascot, the World Cup of 1982 saw the need to upgrade the infrastructures of Spanish television centres and the Spanish National Radio (RNE) stations covering the information. SEMI was responsible for the construction, reinforcement and expansion of many Broadcasting Stations including the Pozo de las Nieves (Las Palmas), Arguís (Huesca), El Viso (Zamora), Torrente (Valencia), and Jaizquíbel (Guipúzcoa) stations, as well as the 46m metal Tower installed on the Torrespaña (Madrid).

Anticipating the present challenge posed by renewable energies, SEMI has been executing “turnkey projects” relating to wind power, photovoltaic energy and thermal solar power for many years. This is a reflection of the company’s commitment to renewable sources and the environment.

The company took a step forward with the design of the EAC-350 overhead line. The project was funded by the MINER and the CDTI and was completed in partnership with the Pontificia de Comillas University, and the Mining Engineering School of the UPM.

This research resulted in the prototype of the overhead line for alternating current and a 350 km/h speed, known as the C-350, which was later accepted and installed on three kilometres of the Madrid-Seville AVE line in order to undergo real tests.

On 15th December 1998, tests were carried out with AVE trains, and they successfully reached and exceeded the speed for which the new overhead line had been designed.

The same year saw the design and construction of the 350 km/h railway overhead line.

The company started construction and reconstruction works for EDF in France, after the storms which had occurred in December 1999.

After a request for international collaboration was issued by EDF, SEMI cooperated by sending staff specialised in high- and very high- voltage works to quickly re-establish the service and reconstruct the French electricity grid.

Years later, SEMI was certified by SDF and permanently established itself in France through the creation of its subsidiary, SEMI France.

In 2002, the company started implementing its international expansion plan. After executing several projects in different countries, SEMI decided to finally establish itself in Morocco, Mexico and Costa Rica.

In 2003, the Railway Infrastructure Manager (GIF) awarded SEMI the “Project, installation and maintenance of the Overhead Contact Line (GIF Polyvalent Overhead line, called Dual Current CPG) on the test stretch of the three-rail track between Olmedo and Medina del Campo”.

This was the first project in which hybrid technologies were applied to satisfy the need for mixed passenger and freight corridors. The corridors were also susceptible to being operated in 3 kV DC and 25 kV AC, as the goal was for them to be certified for all types of European operators.

SEMI’s engineering proposal to solve this problem was the design chosen for the implementation of mixed-traffic lines on the Spanish network.

In 2004, SEMI France became a reality. It was formed as an independent company with great potential, and as a point of support for expansion throughout Europe.

The high-speed system developed by SEMI, with a European interoperability certificate since 2008, became state-of-the-art technology and engineering, suitable to be implemented and exported internationally for similar projects.

Popularly known as “SEMI Venezuela”, in 2009 SEMI expanded its activities through SEDMIVE.

In line with the international strategic plan, SEMI established itself in Italy and Panama through two new companies: SEMI Italia and SEMI Panam'á.

In 2011, the company expanded internationally and SEMI established itself in Germany, Bulgaria, Poland and the Dominican Republic.