Hybrid organic-inorganic solar cell was fabricated by thin film of nanocrystalline magnesium phthalocyanine, MgPc, on ptype Si substrates using the conventional thermal evaporation technique. The measured electrical parameters were used to determine the predominat conduction mechanisms of these heterojunctions in the temperature range 298 to 373 K. The dark forward current was found to be increased exponentially with the applied voltage. Where the dark forward current density-voltage characteristics indicated a thermionic emission conduction over the MgPc/p-Si interface at relatively low voltages followed by a space-charge-limited current (SCLC) controlled by a single dominating trap level of 0.34eV at relatively high voltages. On the other hand, the carrier generation-recombination process limits the reverse current. Also, electrical parameters were determined from the I-V characteristic. The capacitance-voltage characteristics indicated that the junction is of abrupt nature. Under illumination, the cell exhibits photovoltaic characteristics with an opencircuit voltage (Voc) of 0.32 V, a short circuit current (Isc) of 246μA, and a power conversion efficiency η of 2.71%. These parameters have been estimated at room temperature and under illumination of 6 mW/cm2 white light.