High quality transparent cathode is one of the major impediments to achieve high performance semitransparent organic solar cells (OSCs). This work reports a study of the effect of Al/indium tin oxide (ITO) cathode for application in poly(3-hexylthiophene) (P3HT):1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C 60 (PCBM)-based semitransparent OSCs. The power conversion efficiency (PCE) and lifetime of OSCs made with Al/ITO-based cathode are studied and compared with structure identical OSCs made with Ca/Ag/ITO-based cathode. The interfacial properties at polymer/cathode interface were investigated using X-ray Photoelectron Spectroscopy (XPS). It is found that an ultrathin Al:AlOx interlayer was formed at polymer/cathode interface, induced during the ITO deposition. Semitransparent OSCs with Al/ITO cathode having a PCE of up to 2.37% with an average transmittance >40% at light wavelength of 650nm were demonstrated. The results reveal that the presence of an ultrathin AlOx layer at the polymer/cathode interface plays a role in determining the stability of the semitransparent OSCs. The possible designs to improve the performance of semitransparent organic solar cells over the two competing indexes of power conversion efficiency and transmittance are discussed.