| Chai ไชย | |
| King of Ayutthaya | |
| Succession: | King of Siam |
| Reign: | 1655–1656 |
| Full Name: | Chai Sanphet VI |
| Predecessor: | Prasat Thong |
| Successor: | Si Suthammaracha |
| House: | Prasat Thong Dynasty |
| Father: | Prasat Thong |
| Birth Date: | 1630 |
| Death Date: | 1656 |
| Death Place: | Wat Khokphraya, Ayutthaya, Ayutthaya Kingdom |
Chai (Thai: ไชย), full title in Thai Somdet Chaofa Chai (Thai: สมเด็จเจ้าฟ้าไชย) or King Sanpet VI, was a king of Ayutthaya, reigning almost 1 year from 1655 to 1656.
Upon King Prasat Thong’s death in 1655, Chaofa Chai, his eldest son, succeeded his father as King Sanpet VI.
However, it was a Thai tradition gave brothers a higher priority over sons in succession. Prince Si Suthammaracha, Chaofa Chai's uncle, plotted with his nephew, Prince Narai, to bring Chaofa Chai down. After nine months of ascension, Chaofa Chai was executed following a coup.[1] [2] Narai and his uncle marched[3] into the palace, and Si Suthammaracha crowned himself king. Si Suthammaracha appointed Narai as the Uparaja, or the Front Palace.