| Semisi Fonua | |
| Office1: | Speaker of the Legislative Assembly |
| Term1: | 1951–1958 |
| Office2: | Member of the Legislative Assembly |
| Constituency2: | Tongatapu |
| Term2: | 1936–1968 |
| Birth Date: | 1911 |
| Death Place: | Lapaha, Tonga |
| Death Date: | 5 January 1968 |
Semisi Fatafehi Fonua (1911 – 5 January 1968) was a Tongan noble and politician. He held the titles of Kalaniuvalu and Fotofili, and was a member of the Legislative Assembly between 1936 and his death in 1968, serving as Speaker from 1951 until 1958.
Born in 1911 to Fotofili Siosiua and Afa,[1] Fonua was educated at primary school in Niuafoʻou and Tupou College.[2] He was a suitor of Fusipala, but Queen Salote refused to allow them to marry despite the two being engaged.[3] Shortly afterwards he was told to marry Sisilia Tuʻitavake,[3] with the wedding taking place in June 1932.[1] He became Kalaniuvalu in 1935 and took his father's Fotofili title in 1955.[1]
He was elected to the Legislative Assembly in 1936 as one of the Noble representatives for the Tongatapu constituency. He was re-elected in every election until his death in January 1968,[2] also serving as Speaker and vice-president of the Privy Council between 1951 and 1958. One of his sons, Sosi'ua Ngalumoetutulu, later also served as Speaker of the Legislative Assembly.