Ultra-hot Jupiter is a new class of exoplanet that has emerged in recent years. Their extremely high temperatures could cause thermal dissociation of molecules and ionisation of atoms. These planets are ideal laboratories to study the chemistry and physics of planetary atmospheres under extreme conditions. We have detected strong Hα absorption in KELT-9b and KELT-20b as well as ionised calcium in KELT-9b, WASP-33b and KELT-20b for the first time (Yan et al. 2018, 2019, Casasayas-Barris et al. 2019). In this talk, I will present our latest results on UHJ observations, including the detection of hydrogen Balmer lines during the transit of WASP-33b. Particularly, I will present the detection of temperature inversions with atomic Fe lines in the dayside atmospheres of WASP-189b (Yan et al. 2020) and WASP-33b.
