SEMTEX® is a registered trade name for a group of industrial mining and blasting explosives with plastic (mouldable) qualities. Semtex was developed and manufactured by the Explosia Division of the Synthesia Corporation, in Parubice, Semtin, the Czech Republic (formerly western Czechoslovakia).

It was developed in the 1950s with several variations produced through the end of the twentieth century, and is still made. However, its production makes up less than about 1% of the total other explosives production made by Explosia.

Securesearch, Inc. manufactures several inert simulants that replicate the characteristics and colors of different types of Semtex (Semtex-H, Semtex S1A and Semtex 10—each being a different color.) These inert products have x-ray correct characteristics for screener training and testing.