There are at least 3 artists with that pseudonym: (1) Damon Baxter a.k.a. Deadly Avenger produced two straight up electro EPs in '95 and '96 under the name Sem. (2) Semothy Jones, a British record producer. (3) A dance act from Mental Madness Records. (4) Electronic / Future Bass Producer from Netherlands. He continued to release under the name Sem until 2020, and from around 2021 he has been active under the name who's sem. https://soundcloud.com/whosem