A temperature sensor (1) for gas burner (2) having a thermocouple (11) comprising electric conductors (15) and a connection element (12) to connect to the burner (2) associated with a free end (18) of such thermocouple (11), said connection element (12) being suitable for being inserted inside a seat of the sensor (8) formed inside a wall (4) of the burner (2) and having a first end (26) suitable for being placed at the outer surface (6) of the burner (2), said thermocouple (11) being inserted inside a blind hole (29) of the connection element (12) which opens at a second end (28) of said connection element (12). Said blind hole (29) ends with at least one part (31) convergent towards an end zone (K) of the hole (29), said part (31) getting in contact with the thermocouple (11) inserted inside the connection element, the connection element (12) being made from an iron-chrome-aluminum alloy. An assembly comprising such temperature sensor and a burner is also claimed.