Significance We demonstrate that engineering of two-dimensional molybdenum carbide/disulfide heterostructures can result in superconducting architectures with higher critical temperatures than that of pristine α-Mo ₂ C. We developed a gas-phase reaction approach for the heterostack formation via phase transitions, which involves short sulfurization times (1–5 min) of α-Mo ₂ C films. Heterostructures of α-Mo ₂ C and γ′-phase MoC _1−x exhibit superconductivity with a higher critical temperature ( T _C ∼ 6.8 K) than the original Mo ₂ C crystal ( T _C ∼ 4.0 K). The distinct chemical composition and modified structure of the metastable γ′-MoC _1−x phase present in the layered structure might lead to a higher interfacial density of states and increase in the frequency of the relevant phonon modes, thus contributing to the superconductivity and hence to a higher T _C .