This book reports the fabrication and electrical characterization of zinc phthalocyanine (ZnPc), copper phthalocyanine (CuPc) and nickel phthalocyanine (NiPc) based devices. The fabrication and electrical (both DC and AC) characterization of schottky diodes based on organic semiconductor ZnPc, modified by inorganic material molybdenum oxide (MoO3) is undertaken. Employing direct current and low signal impedance spectroscopy, the conduction mechanisms in the three devices containing ZnPc, an interfacial layer of MoO3 and ZnPc doped with MoO3 are investigated and compared. In a parallel work, Al/p-CuPc/Ni samples were fabricated. I-V characteristics were evaluated at 24oC and 64oC. It was found that dark current-voltage characteristics of the Al/p-CuPc/Ni samples are non-linear and show rectification behavior. This monograph also reports the experimental results for the humidity dependent properties of an organic field effect transistor based on copper phthalocynanine (CuPc). In the last part of current study the effect of humidity on capacitance and resistance of the Ag/PEPC/NiPc/ZnO/Ag sensors is investigated at two different frequencies of the applied voltage: 120 Hz and 1 kHz.