This proposal is a continuation of our recent proposal RB 610004 where this partcurrent measurements) was not completed due to the reduced beam intensity. Currents experiment are necessary to complete our muSR studies of semi-imsulating GaAs at ISIS, PSI and TRIUMF facilities. As a goal of the experiment we hope to obtain unique (due to the time and length scale) information on charge dynamics of deep centers in GaAs and to demonstrate the power of the muSR measurements as a tool to study fundamental properties of the host.