Logarithmic plots of current or carrier concentration vs inverse temperature in semi-insulating GaAs samples are nearly always well characterized by straight lines with a donor activation energy of 0.76 +/- 0.02 eV, as long as the surfaces are well polished or etched and the edges are cleaved. However, edges cut with common dicing saws produce an excess conductance which can dominate the bulk conductance at room temperature and below. This excess conductance is due to carrier hopping between defects in a surface layer of approximately 2000angstrom thickness, which can be easily removed by etching. Some polished surfaces also exhibit this same effect.