Using the methods of scanning probe microscopy, I-V characteristics of individual In _x Ga _1-x As nanowires with different In content (x) were measured. A sharp decrease in the conductivity was observed at x=0.7. It is shown that type of contact between nanowire and probe changes from ohmic at x=1 to Schottky at x=0.85. These changes were explained by the formation of surface conductive channel, induced by surface Fermi level pinning in conduction band for x>0.85.