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In this paper we report on the spectral evolution of 4U 1608-522 performed aspart of the long Galactic Bulge monitoring with INTEGRAL. The data set includethe April 2005 outburst. BeppoSAX archival data (two observations, in 1998 and2000) have been also analysed and compared with the INTEGRAL ones. Threedifferent spectral states have been identified from the hard Color-Intensitydiagram derived from INTEGRAL: the canonical Hard and Soft as well as anIntermediate state. The hard state spectrum is well described by a weak blackbody component plus a Comptonised plasma component with high electrontemperature (kTe~60 keV) extending up to 200 keV without any additionalcut-off. The soft spectra are characterized by a cold Comptonised plasma (kTe=2-3 keV, and 7 keV for the intermediate state) and a strong disk black bodycomponent. A reflection component, indicating reflection of the X-ray radiationfrom the accretion disc, is also present in the soft state revealed by BeppoSAXin 1998. The 2000 BeppoSAX observation revealed the source in quiescent statemodelled by a neutron star atmosphere (assuming a neutron star with radius 10km and mass 1.4 Msun) with an effective temperature, kTeff of 0.1 keV plus apower law component with Gamma~3 detected for the first time for this source.This spectrum can also be modelled with a simple black body compatible withemission originating from a small fraction of the NS surface of radius of 0.4km.

INTEGRAL and BeppoSAX observations of the transient atoll source 4U 1608-522: from quiescent to hard spectral state