Temperature and magnetic-field dependence of the conductivity of YBa 2 Cu 3 O 7−δ films in the vicinity of superconducting transition: Effect of T C -inhomogeneity Temperature and magnetic field dependences of the conductivity of YBa2Cu3O 7−δ films in the transition region are analyzed taking into account spatial inhomogeneity in transition temperature, Tc. (i) An expression for the superconducting contribution to conductivity, σs(T, H, Tc), of a homogeneous superconductor for low magnetic fields, H ≪ Hc2 (0) (ii) The error in σs(T, H, Tc) occurring due to the presence of Tc-inhomogeneity is calculated and plotted on an H − T plane diagram. These calculations use an effective medium approximation and a Gaussian distribution of Tc. (iii) Measuring the temperature dependences of a voltage, induced by a focused electron beam, we determine spatial distributions of the critical temperature for YBa2Cu3O 7−δ microbridges with a 2 µm resolution. A typical Tc-distribution dispersion is found to be ≈1 K. For such dispersion, error in σs(T, H, Tc) due to Tc-inhomogeneity exceeds 30% for magnetic fields H < 1 T and temperatures |T − Tc| < 0.5 K . (iv) Experimental R(T, H) dependences of resistance are well described by a numerical solution of a set of Kirchoff equations for the resistor network based on the measured spatial distributions of Tc and the expression for σs(T, H, Tc).