Methanol masers at 6.7GHz are known to be tracers of high-mass star formation in our Galaxy. In this paper, we study the large-scale physical conditions in the star-forming clumps/cores associated with 6.7GHz methanol masers using observations of the (1,1), (2,2), and (3,3) inversion transitions of ammonia with the Effelsberg telescope. The gas kinetic temperature is found to be higher than in infrared dark clouds, highlighting the relatively evolved nature of the maser sources. Other than a weak correlation between maser luminosity and the ammonia line width, we do not find any differences between low- and high-luminosity methanol masers.