We observe magnetic quantum oscillations in the heat capacity of the Kondo insulator ${\mathrm{YbB}}_{12}$. The frequency of these oscillations, $F=700\mathrm{T}$, agrees with that from magnetoresistance and torque magnetometry experiments for ${\mu }_{0}H>35\mathrm{T}$ in the Kondo insulating phase. Remarkably, the quantum-oscillation amplitudes in the heat capacity are substantial, with $\mathrm{\Delta }\tilde{C}/T\approx 0.5\mathrm{mJ}{\mathrm{mol}}^{-1}{\mathrm{K}}^{-2}$ at 0.8 K, accounting for 13% of the known linear heat-capacity coefficient $\gamma$. Double-peak structures of quantum-oscillation amplitudes due to the distribution function of fermions were identified and used to determine the value of the effective mass from the heat capacity, which agrees well with that from torque magnetometry. These observations support bulk charge-neutral fermions contributing to the quantum oscillations in ${\mathrm{YbB}}_{12}$.

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• Specific heat
• Kondo insulators