  We present the analysis of the high energy emission of the Galactic black
hole GRO J1655-40 at the beginning of its 2005 outburst. The data from 458 ks
of INTEGRAL observations, spread over 4 weeks, are analyzed, along with the
existing simultaneous RXTE and Swift data. The high energy data allow us to
detect the presence of a high energy cut-off and to study its evolution during
the outburst rise. This high energy feature is generally related to thermal
mechanisms in the framework of Comptonization models from which we can estimate
the plasma parameters. We found an electron temperature of about 30-40 keV and
an optical depth around 1.8-2.1. The high energy cut-off decreased along with
the radio flux, and disappeared as the jet turned off.
