Bulk GaAs crystals were grown by synthesis solute diffusion (SSD) technique in a wide range of growth temperatures between 990 and 1150 degrees C. Electrical properties of these crystals were studied by means of van der Pauw, admittance spectroscopy, deep levels transient spectroscopy and photoinduced current spectroscopy techniques. It was shown that the main defects determining the properties were the GaAs antisites acceptors and the A center acceptors with the levels, respectively, E-v +0.078 eV and E-v +0.43 eV. The conductivity of the grown crystals was p-type and showed a pronounced maximum at a level of 10(4)-10(5) Omega cm for growth temperatures between 1020 and 1080 degrees C. If the crystals were additionally compensated either by unintentional Si donors contamination from quartz crucibles or by intentional light Te doping one could get semi-insulating material with the room temperature resistivity higher than 10(6) Omega cm. The Fermi level in such crystals was pinned near E-c -0.8 eV, i.e. close to the EL2 donors. Measurements by deep levels transient spectroscopy on n-type doped crystals or by low frequency capacitance-voltage on semi-insulating crystals showed that the density of EL2 in these samples was in the low 10(14) cm(-3) and that thus the EL2 donors were not the main compensating agents. (c) 2007 Elsevier Ltd. All rights reserved.