In this study, stacked graphene diodes were fabricated via direct bonding using single-crystal graphene on a SiC substrate. Switching and S-shaped negative resistance were observed in the junction electrical properties measured via the 4-terminal configuration. The high-resistance state switched to the low-resistance state after applying a maximum junction voltage of ~10 V. In the high-bias voltage region, the junction voltage decreased from the maximum junction voltage to a few volts, indicating a negative resistance. In the high-resistance state, junction conductance was nearly constant at 0.13 mS. Electrical conductance in the high-bias region was expressed using an exponential function with an exponent of −1.26. Therefore, the fabricated stacked graphene diode with a simple device structure demonstrated strong nonlinear electrical properties with negative differential conductance.