In this paper, a film of n-ZnO nanowalls was deposited over p-silicon (Si) substrate by thermally evaporating metallic zinc powder in oxygen gas environment. Several techniques were used to examine various properties of prepared ZnO nanowalls. The morphological study confirmed that the grown ZnO film possesses nanowalls shaped morphologies containing three dimensional (3D) interconnected nanowalls forming large voids with irregular shapes. Interestingly, whole Si substrate was covered with nanowalls shaped morphologies. The structural characterizations examined by x-ray diffraction (XRD) confirmed that the deposited nanowalls possess wurtzite hexagonal crystal structure. The presence of a strong UV and suppressed green emissions at room-temperature photoluminescence (PL) spectrum exhibited good optical properties of the deposited nanowalls. The electrical properties of the deposited n-ZnO nanowalls over p-silicon substrate assembly was examined in both forward and reverse bias conditions at room-temperature. The fabricated heterojunction device exhibits a standard rectifying behavior which manifests itself in an exponential increase of the current with increase in voltage at forward bias condition. Also, it has a good quality factor similar to an ideal diode.