ZnO nanowires/p-Si heterojunction diodes are fabricated by employing low temperature double-step chemical bath deposition technique. The grown samples are initially annealed at different temperatures in the range of 300 °C to 600 °C at 10 psi argon atmosphere for 30 min. Field emission scanning electron microscope images confirmed the growth of vertically oriented ZnO nanowires with average nanowire diameter and height of 183–190 nm and ~1.4 μm, respectively. The x-ray diffraction study shows that the samples are poly-crystalline with hexagonal wurtzite structure and ZnO nanowires are vertically c-axis oriented. The photoluminescence study indicates the presence of oxygen vacancy in as-grown and 300 °C annealed sample, whereas, the 500 °C annealed ZnO nanowires show the existence of oxygen interstitials. Heterojunction diodes are fabricated on the as-grown, 300 °C, 400 °C, 450 °C, 460 °C, 475 °C, 490 °C, 500 °C, 550 °C and 600 °C annealed nanowires for the measurements of current-voltage and capacitance-voltage characteristics. Both the results indicate an electron dominated transport for the as-grown to 490 °C samples and hole transport for ≥500 °C annealed sample. The acceptor or p-type dopant formation temperature is observed to be 500 °C, which shows an effective acceptor concentration of 1.15 × 1015 cm−3 (at 10 kHz) and 1.74 × 1015 cm−3 (at 1 MHz). Thus the work indicates a possible route for converting the n-type ZnO nanowires to p-type of nature. © 2018