摘要： The threshold voltages at the onset of conduction for electron and hole branches can provide information on band gap values or the interface states in a gap. We measured conductivity of bilayer graphene encapsulated by hexagonal boron nitride as a function of back and top gates, where another bilayer graphene is used as a top gate. From the measured conductivity the transport gap values were extracted assuming zero interface trap states, and they are close to the theoretically expected gap values. From a little discrepancy an average density of interface states per energy within a band gap (Dit) is also estimated. The data clearly show that Dit decreases as a bilayer graphene band gap increases rather than being constant. Despite the decreasing trend of Dit, interestingly the total interface states within a gap increases linearly as a band gap increases. This is because of ~ 2 × 1010 cm-2 interface states localized at band edges even without a band gap, and other gap states are equally spread over the gap.