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 .