Heteroepitaxial undoped ZnO films were grown on Si(100) substrates by radio-frequency reactive sputtering, and then some of the samples were annealed at N2-800℃(Sample 1,S1) and O_2-800℃(Sample 2,S2) for 1h,respectively.The electrical transport characteristics of a ZnO/p-Si heterojunction were investigated.We found two interesting phenomena.First,the temperature coefficients of grain boundary resistances of S1 were positive(positive temperature coefficients,PTC) while that of both the as-grown sample and S2 were negative(negative temperature coefficients,NTC).Second,theⅠ-Ⅴproperties of S2 were similar to those common p-n junctions while that of both the as-grown sample and S1 had double Schottky barrier behaviors,which were in contradiction with the ideal p-n heterojunction model.Combined with the deep level transient spectra results,this revealed that the concentrations of intrinsic defects in ZnO grains and the densities of interfacial states in ZnO/p-Si heterojunction varied with the different annealing ambiences,which caused the grain boundary barriers in ZnO/p-Si heterojunction to vary.This resulted in adjustment electrical properties of ZnO/p-Si heterojunction that may be suitable in various applications. Heteroepitaxial undoped ZnO films were grown on Si (100) substrates by radio-frequency reactive sputtering, and then some of the samples were annealed at N2-800 ° C (Sample 1, S1) and O_2-800 ° C 1h, respectively. The electrical transport characteristics of a ZnO / p-Si heterojunction were investigated. We found two interesting phenomena. First, the temperature coefficients of grain boundary resistances of S1 were positive positive temperature coefficients (PTC) while that of both the as-grown sample and S2 were negative (negative temperature coefficients, NTC). Second, the I-V properties of S2 were similar to those common pn junctions while that of both the as-grown sample and S1 had double Schottky barrier behaviors, which were in contradiction with the ideal pn heterojunction model. Covered with the deep level transient spectra results, this revealed that the concentrations of intrinsic defects in ZnO grains and the densities of interfacial states in ZnO / p-Si heterojunction varied with the different annealing ambiences, which caused the grain boundary barriers in ZnO / p-Si heterojunction to vary.This resulted in adjustment electrical properties of ZnO / p-Si heterojunction that may be suitable in various applications.