In this study, we present a detailed investigation of the electrical and dielectric properties of the Au/Si3N4/n-Si (MIS) structures. The capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics have been measured in the frequency range of 1 kHz-1 MHz at room temperature. Calculation of the dielectric constant (ε'), dielectric loss (ε''), loss tangent (tanδ), ac conductivity (σac) and complex electric modulus (M*) are given in the studied frequency ranges. Experimental results show that the decrease of ε' and ε'' with the increasing frequency are observed. In addition, the increase of σac with the increasing frequency is founded. Also, electric modulus formalism has been analyzed to obtain the experimental dielectric data. In addition, interfacial polarization can be more easily occurred at the lower frequency and/or with the number of interface state density between Si3N4/Si interface, consequently, contribute to the improvement of dielectric properties of MIS structure.