We examine the temperature-dependent electrical conductivity in amorphous InGaZnO thin films with Various cation compositions. In-rich films are metallic, while Ga-rich films are semiconducting with logarithmic conductivities linear to -T-1/4 above T = 60K. The Zn-rich films are also semiconducting but have >10(2) times higher conductivity than the Ga-rich films. At T > 60 K, thermal electronic excitation dominantly contributes the conduction, while at T < 60 K, certain impurity scatterings or structural disorders have importance in the electrical properties in low carrier a-IGZO system.