We report on the X-ray spectrum of the 401 Hz X-ray pulsar and type I burst source SAX J1808.4-3658 during its 1998 April/May hard outburst .
The observations were made with RXTE over a period of three weeks .
The spectrum is well-described by a power law with photon index 1.86 \pm 0.01 that is exponentially cut off at high energies .
Excess soft emission above the power law is present as well as a weak Fe-K line .
This is the first truly simultaneous broad-band ( 2.5–250 keV ) spectrum of a type I burst source in the hard state .
The spectrum is consistent with other hard state burster spectra which cover either only the soft ( 1–20 keV ) or hard ( \buildrel > \over { \sim } 20 keV ) bands , or cover both , but not simultaneously .
The cut-off power law spectrum resembles that of black hole candidates ( BHCs ) in their low states , observed with RXTE .
We compare the SAX J1808.4-3658 spectrum to three BHCs and find that the power law is somewhat softer .
This suggests that the photon index may provide a way to distinguish between low state emission from Galactic black holes and type I bursters .