In this work, we report a single crystalline p-Si/(001) $\beta $ -Ga2O3 heterojunction diode fabricated using semiconductor grafting technology. The diode showed a breakdown voltage ( $\text{V}_{\text {br}}{)}$ of ~0.86 kV, which is the highest breakdown voltage reported for Si/(001) Ga2O3 heterojunction diode to date. The average peak electric field ( $\text{E}_{\text {m}}{)}$ was calculated to be >2 MV/cm near breakdown, while the specific on resistance ( $\text{R}_{\text {on}{,\text {sp}}}{)}$ was measured to be 7.7 $\text{m}\Omega \cdot $ cm2, corresponding to a power figure of merit of ~96 MW/cm2. Catastrophic breakdown is confirmed by optical microscope inspection. The turn on voltage ( $\text{V}_{\text {on}}{)}$ of the diode was measured to be around 1.12 V, the on–off ratio was calculated to be $9\times 10^{{9}}$ at–2 and 2 V, and the ideality factor was extracted to be approximately 1.18. The band structure of the diode was analyzed, and C-V measurements were also performed to understand the trapping behavior at the Si/Ga2O3 interface.