Magnesium phthalocyanine (MgPc) based Schottky diode on indium tin oxide (ITO) substrate was fabricated by thermal evaporation method. The dark current voltage characteristics of the prepared ITO–MgPc–Al heterojunction Schottky diode  were measured at different temperatures. The diode showed the non-ideal rectification behavior under forward and reverse bias conditions with a rectification ratio (RR) of 56 at ±1 V at room temperature. Under forward bias, thermionic emission and space charge limited conduction (SCLC) were found to be the dominant conduction mechanisms at low (below 0.6 V) and high voltages (above 0.6 V) respectively. Under reverse bias conditions, Poole–Frenkel (field assisted thermal detrapping of carriers) was the dominant conduction mechanism. Three different approaches namely, I–V plots, Norde and Cheung methods were used to determine the diode parameters including ideality factor (n), barrier height (Φ_b), series resistance  (R_s) and were compared. SCLC mechanism showed that the trap concentration is 5.52 × 1022 m−3 and it lies at 0.46 eV  above the valence band edge.