Realization of a three-dimensional (3D) analog of graphene has been a central challenge in topological materials science. Graphene is stabilized by covalent bonding, unlike conventional spin-orbit-type 3D Dirac semimetals (DSMs). In this study, we demonstrate the material realization of covalent-type 3D DSMs $R_8\mathrm{Co}{X}_3$ stabilized by covalent bonding. We confirm the clean Dirac semimetal state in ${\mathrm{Y}}_8{\mathrm{CoIn}}_3$ by combined thermodynamic and transport experiments. We also realize high carrier mobility exceeding $3000{\mathrm{cm}}^2/\mathrm{Vs}$ even in polycrystalline samples of $R_8\mathrm{Co}{X}_3$. Our research provides a material platform for exploration of Dirac electrons in three dimensions with wide chemical tunability.

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• Dirac semimetal
• Density functional theory
• Resistivity measurements