A heterojunction of p-Si(100)/n-ZnO nanorods was fabricated by a simple hydrothermal method. The photocatalytic activity of this heterojunction was examined by degradation of Rhodamine B (RhB) under UV light irradiation. The results indicated that the p-Si(100)/n-ZnO nanorods heterojunction exhibits higher photocatalytic activity compared to that of a glass/n-ZnO nanorods. The inner electric field created by the space charge region of heterojunction will oppose the recombination of photogenerated electrons and holes. Furthermore, this heterojunction serves as a convenient recyclable and effective photocatalyst. The photodecomposition rate of RhB after 5 cycles is negligible change in an experiment using this heterojunction. •A heterojunction of p-Si/n-ZnO NRs was fabricated by a simple hydrothermal method.•An improvement in photocatalytic activity of the heterojunction was demonstrated.•The enhancement is attributed to the inner electric field and effective surface area.•This heterojunction serves as a convenient recyclable and effective photocatalyst.