The aromatic thermosetting copolyester (ATSP) was deposited on p-Si substrates by the spin coating method, and the thickness of thin film layer was about 50 nm. It was employed to fabricate metal-polymer-semiconductor (MPS) heterojunctions as interfacial layers between metal contact and p type Si. The morphological properties of the Al/ATSP/p-Si heterojunctions were investigated by Scanning Electron Microscope (SEM) and an Atomic Force Microscope. The electrical characteristics of the heterojunctions were analyzed within a wide temperature range between 100 K and 500 K and frequency range. The current-voltage-temperature (I-V-T) characteristics of the MPS heterojunctions were explained by the Thermionic Emission (TE) theory and Norde function. Critical electrical parameters including leakage current (I-0), barrier height (phi(b)) and ideality factor (n) and series resistance (R-s) were calculated by I-V-T characteristics in dark conditions. The value of n and phi(b) was obtained as 2.56 and 0.78 eV at 300 K. The n and phi(b) values were obtained as strong function of the temperature depending on barrier inhomogeneity. The temperature dependent rectification ratios of the Al/ATSP/p-Si heterojunctions were calculated and discussed in the details considering effective operating temperatures. The capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics were measured at 300 K. To obtain Fermi energy (E-F), donor concentration (N-a), maximum electric field (E-m), phi(b) and interface states (N-ss), were performed on the bases of voltage and frequency at 300 K. From the electrical analysis results, it is proposed that the MPS device can be employed in electronic devices at low and high temperatures.