Niels Arntzen Sem (10 February 1782–19 December 1859) was a Norwegian politician. He was elected to the Norwegian Parliament in 1825 and 1827, representing the constituency of Stavanger Amt. He worked as district magistrate (sorenskriver) for Jæren from 1823 until 1828. In 1830 and 1845 he was President of the Storting, sharing the position with several people.