We derived the stellar parameters of a sample of Galactic early-O type stars by analysing their UV and Far-UV spectra from FUSE ( 905-1187Å ) , IUE , HST-STIS and ORFEUS ( 1200-2000Å ) .
The data have been modeled with spherical , hydrodynamic , line-blanketed , non-LTE synthetic spectra computed with the WM-basic code .
We obtain effective temperatures ranging from T _ { eff } = 41,000 K to 39,000 K for the O3-O4 dwarf stars , and T _ { eff } = 37,500 K for the only supergiant of the sample ( O4 If ^ { + } ) .
Our values are lower than those from previous empirical calibrations for early-O types by up to 20 % .
The derived luminosities of the dwarf stars are also lower by 6 to 12 % ; however , the luminosity of the supergiant is in agreement with previous calibrations within the error bars .
Our results extend the trend found for later-O types in a previous work by Bianchi & Garcia .