The semis (literally meaning half) was small Roman bronze coin that was valued at half an as. During the Roman Republic, the semis was distinguished by an 'S' (indicating semis) or 6 dots (indicating a theoretical weight of 6 uncia). The coin featured a bust of Saturn on the obverse, and the prow of a ship on the reverse.

Initially a cast coin, like the rest of Roman Republican bronzes, it began to be struck from shortly before the Second Punic War (218-204 BC). The coin was issued infrequently during the Roman Empire, and ceased to be issued by the time of Hadrian (117-138 AD).

See also: Roman currency.