SEM or Sem can refer to:

• Search engine marketing, promoting websites by increasing their visibility in search engine results
• Security event manager, a security log tool used on data networks

• Stock Exchange of Mauritius, the principal stock exchange of the island country of Mauritius
• Strategic enrollment management, an element of planning for new growth at a university or college
• Samsung Electro-Mechanics, a South Korean company

• Single Electricity Market, the integration of the electricity sectors of the Republic of Ireland and Northern Ireland in a single market
• Strategic energy management, continuous improvement process for energy efficiency based on behavioral change

• Structural equation modeling, in data analysis
• Simultaneous equations model, in econometrics
• Standard error of the mean in statistics

• Craig Field (Alabama) (IATA code: SEM), a public airport four miles southeast of Selma, in Dallas County, Alabama
• Sem, Ariège, a former commune in the Ariège department in southwestern France
• Sem, Norway, a village in Tønsberg Municipality in Vestfold county, Norway
• Sem Municipality, a former municipality in Vestfold county, Norway

• Scanning electron microscope
• Space Experiment Module, of the Freestar experiment on space shuttle Columbia
• Synthesizer expansion module in an Oberheim Electronics synthesizer
• Sistema Eléctrico de Magallanes, an electrical power grid of Chile
• SEM, instrument (seismometer) of the Surface Science Platform (Kazachok) mission ExoMars 2022
• A protecting group in organic chemistry, see 2-(trimethylsilyl)ethoxymethyl chloride (SEM-Cl)

• Society for Experimental Mechanics, an engineering professional organization.
• The School of Ecclesiastic Music the school of Byzantine Music in Mount Lebanon
• Swedish Evangelical Mission
• Society for Ethnomusicology, an ethnomusicology in Indiana, US
• Science and Engineering Magnet, a school in Dallas, Texas, US
• S.E.M. Group civil engineering company based in South Australia
• Steam Engine Makers' Society, early British trade union
• Shandong Engineering Machinery, owned by Caterpillar Inc.
• State Secretariat for Migration (Switzerland)

• Shem or Sem, one of the sons of Noah, as depicted in the Bible
• Sem (given name), a usually masculine given name
• Sem (artist) (1863–1934), French caricaturist
• Elise Sem (1870–1950), Norwegian barrister, women's activist, and sports official
• Ingebjørg Dahl Sem (born 1938), Norwegian Christian writer
• Ingebjørg Sem (1931–2009), Norwegian actress
• John Sem (born 1973), Papua New Guinean Olympic boxer
• Niels Arntzen Sem (1782–1859), Norwegian politician
• Suy Sem (born 1947), Cambodian politician

• Super Étendard Modernisé, a French fighter aircraft
• Self-evaluation maintenance theory, a psychological theory of self
• New Austrian tunnelling method or Sequential Excavation Method
• Sports and exercise medicine