In recent years, some concerns about halogen (Cl, Br, and F)-related high-temp. corrosion in biomass- or waste-fired boilers have been raised. The presence of alkali chlorides in the deposits is believed to play a major role in high-temp. corrosion of the superheater steel materials in biomass- or waste-fired boilers. Available data are very scarce regarding alkali-bromide- or -fluoride-induced corrosion. This work has carried out using lab-scale high-temp. corrosion tests with three different superheater tube materials (10CrMo9-10, AISI 347, and Sanicro 28) exposed to KBr or KF at different temps. (400-600 °C). At relatively low temps. (≤550 °C), KBr and KF showed corrosivity similar to that of KCl. At 600 °C, KF showed much stronger corrosivity than either KBr or KCl, esp. in the cases with the low-alloy steel 10CrMo9-10 and the austenitic steel AISI 347. At 550 °C and above, the oxide layers formed on the three steels were generally thicker and more uneven when exposed to KF compared to the results of the tests with KBr.