Sem is, together with Jonathan and Hugo van Heemstra, founding partner of Rohe Advocaten. He taught international students intellectual property law at the Hogeschool Inholland and the Nyenrode New Business School for a long time. Since October 2016, Sem also works as senior lawyer and Data Protection Officer at the Dutch Copyright Supervisory Board (CvTA). Further, he is vice-chairman at public broadcasting corporation HUMAN. From 1994 to 2009, Sem worked as a professional musician and was a member of the band “Caesar”. Sem regularly scores syncs in American films, commercials, sport programs and television series, for example in Suits.