Cu/Si composite may be a novel and high-performance material for electronic packaging if the advantages of copper and silicon components are preserved. Because of the severe diffusional reaction between copper and silicon at elevated temperature, efforts are impeded to achieve a bulk Cu/Si composite. Here, by coating a sol-gel-derived Al2O3 film on the Si particle surface, the bulk Cu/Si composites were obtained by the powder metallurgy method. In the prepared Cu/Si composite, Cu forms a continuous matrix while Si particles are homogeneously dispersed in Cu matrix. High-resolution transmission electron microscopy observation indicates that only weak interfacial reaction occurs at the Cu/Al2O3/Si interface and forms a narrow interfacial reaction zone. The thermal diffusivity of the composite at 25 °C is about 30.6 mm2 s−1, over 10 times larger than that of Cu/Si material without Al2O3 film.