We report the effect of metal–insulator transition on electrical transport properties in manganite-based p–i–n heterojunctions, consisting of p-type La0.67Sr0.33MnO3−δ/Pr0.7Ca0.3MnO3−δ and n-type Si with a buffer layer of SiO2. As the temperature is higher than the metal–insulator transition temperature TMI of manganite films, the current–voltage relation of these p–i–n junctions shows good forward rectifying behaviour. Once the temperature is below TMI, the La0.67Sr0.33MnO3−δ/SiO2/Si p–i–n junction behaves like a backward diode. This backward diode-like behaviour in p–i–n junctions based on manganite can be understood by the change in electronic band structure of manganite films with temperature. We also found that the electric current in these p–i–n junctions is dominated by the tunnelling process at higher bias voltages and the space-charge-limited current process at lower bias voltages in these heterojunctions. This work reveals the various properties and the key role of metal–insulator transition in manganite based diodes.