RF magnetron sputtering was used to grow silicon nitride (Si3N4) thin film on GaAs substrate to form metal-oxide-semiconductor (MOS) capacitor. Complex dielectric permittivity (epsilon*), complex electric modulus (M*) and complex electrical conductivity (sigma*) of the prepared Au/Si3N4/p-GaAs (MOS) capacitor were studied in detail. These parameters were calculated using admittance measurements performed in the range of 150 K-350 K and 50 kHz-1 MHz. It is found that the dielectric constant (epsilon ') and dielectric loss (epsilon '') value decrease with increasing frequency. However, as the temperature increases, the epsilon ' and epsilon '' increased. Ac conductivity (sigma(ac)) was increased with increasing both temperature and frequency. The activation energy (E-a) was determined by Arrhenius equation. Besides, the frequency dependence of sigma(ac) was analyzed by Jonscher's universal power law (sigma(ac) = A omega(s)). Thus, the value of the frequency exponent (s) were determined.