The study concerns the C/omega-V performances and examination of dielectric response of MgPc/GaAs organic heterojunction (OHJ) structure of solar energy applications. Throughout this work, many characterizations have been achieved and various parameters have been extracted. C/omega-V and G/omega-V plots are subject to give much knowledge about the mechanism and behavior inside the OHJ. It is revealed that capacitance of OHJ increases with voltage defining deep depletion (dd), depletion (dep) and accumulation (ac) regions. Besides, Ac conductivity at room temperature increases with frequency in particular within the forward biasing voltage, reaching a high point of 28 x 10(-7) S/cm at 5 V. Real and imaginary terms of complex dielectric constant or well known by permittivity, epsilon versus ln omega are studied inside the 1.5V-2.5 V range. The real and imaginary parts of the impedance are found to be frequency dependence within the 1.5 V and 2.5 V bias range. Ac current conductivity sigma(Ac) against frequency (ln omega) of MgPc/GaAs OHJ inside 1.5V-2.5 V bias voltage range is well detailled; the average of conductivity about 8 x 10(-7) S/cm is then recorded. The impedance spectroscopy study is evidenced by the complex impedance M where real and imaginary part are M' and M ''. Profile of M' and M '' as function of voltage exhibits peaks for 3 kHz-300kHz frequency range. It is indicated that M '' and M' are roughly comprised between 0.08 and 1.12 and 0 and 2 respectively. Conduction mechanism is then determined by ln sigma-ln omega plots. The Cole-Cole diagram displays different curves of impedance as distinct semicircle for measured frequencies.