We report on results of a target of opportunity observation of the X-ray transient XTE J1118+480 performed on 2000 April 14–15 with the Narrow Field Instruments ( 0.1–200 keV ) of the BeppoSAX satellite .
The measured spectrum is a power law with a photon index of \sim 1.7 modified by an ultrasoft X-ray excess and a high-energy cutoff above \sim 100 keV .
The soft excess is consistent with a blackbody with temperature of \sim 40 eV and a low flux , while the cut-off power law is well fitted by thermal Comptonization in a plasma with an electron temperature of \sim 10 ^ { 2 } keV and an optical depth of order of unity .
Consistent with the weakness of the blackbody , Compton reflection is weak .
Though the data are consistent with various geometries of the hot and cold phases of the accreting gas , we conclude that a hot accretion disk is the most plausible model .
The Eddington ratio implied by recent estimates of the mass and the distance is \sim 10 ^ { -3 } , which may indicate that advection is probably not the dominant cooling mechanism .
We finally suggest that the reflecting medium has a low metallicity , consistent with location of the system in the halo .