We fabricated p-Si/n-Ga2O3 and p+-Si/n-Ga2O3 heterostructures by surface-activated bonding (SAB) and investigated their electrical properties. Current density–voltage measurement was performed before and after thermal annealing at 450 °C. The current density substantially increased after annealing, which was attributed to thinning of an intermediate layer formed by the bonding process. Distinctive two-stage capacitance–voltage characteristics were observed for p-Si/n-Ga2O3 heterostructures, which were well reproduced by numerical calculation considering the effect of two-dimensional electron gas formed at the heterointerface. These results indicate that Ga2O3-based p–n heterostructures with good interface properties and large-area uniformity can be fabricated using SAB.