The ZnO films have been deposited on p-type silicon (p-Si) substrates using a microwave assisted chemical bath deposition (MW-CBD) method without any template from an aqueous alkaline bath containing zinc nitrate and hexamethylenetetramine as the complexing agents. The ZnO films were synthesized by using mixed aqueous solutions irradiated for 8 min under microwave radiation at 300, 600, 900 and 1200 W. The effect of the microwave power on the morphological and structural properties of zinc oxide (ZnO) films has been investigated. The morphologies of the films have been characterized by field emission scanning electron microscope (FESEM). It was shown that the microwave power influenced the density and orientation of the nanorods. The effects of microwave power on the crystalline structure and orientation of the films were investigated by X-ray diffraction (XRD) method. As a result of the XRD spectra, an improvement in the crystalline quality of the films was observed with increasing in microwave power. The lattice constants, crystal lattice distortion degree and texture coefficient were calculated from XRD data. The diffuse reflectance spectrum of the ZnO nanorod film irradiated at 1200 W was measured and the band gap of this film was estimated from the maximum of the first derivative of this spectrum. The band gap value was also determined using Kubelka-Munk theory. These values determined by derivative analysis and Kubelka-Munk are 3.27 eV and 3.22 eV, respectively. The electrical properties of nanorod ZnO/p-Si heterojunction diode were investigated at room temperature via the current-voltage (I-V). The modified Norde's function combined with conventional forward I-V method was used to obtain the parameters including the series resistance and barrier height (BH).