Metallic and semiconducting states of layered organic materials such as κ-ET₂X salts are analyzed on the basis of bis(ethylenedithio)tetrathiafulvalene molecule (BEDT-TTF, hereafter ET) with essential intraET correlations of electrons. The insulator-metal phase transition of the Mott-Hubbard kind is derived in agreement with available experimental data. Taking into account the Fermi-surface topology the d-wave symmetry of superconducting order parameter is concluded and superconducting phase characteristics are calculated. The obtained value of 2Δ_O/T_c exceeds the BCS one. The results are in agreement with measured nonactivated temperature dependencies of superconducting specific heat and NMR-relaxation rate of central carbons ¹³C in ET.