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Two‐dimensional (2D), high‐temperature, half‐metal ferromagnetic semiconductors with large spin gap and topological band structures are highly desirable for novel nanoscale spintronic applications. A family of stable 2D honeycomb‐Kagome Cr2X3 (X=O,S,Se) monolayers is proposed through first‐principles calculations. Buckled Cr2O3 is a ferromagnetic semiconductor with large out‐of‐plane magnetocrystalline anisotropy energy and a predicted Curie temperature of 332 K under moderate biaxial tensile strain. Planar Cr2S3 and Cr2Se3 are ferromagnetic half‐metals with mirror‐symmetry‐protected nodal lines for spin‐down channel and large direct gap (4.59 and 4.76 eV) for spin‐up channel. The Fermi velocities for Cr2S3 and Cr2Se3 are 2.1×105 and 1.5×105 m s−1, respectively, which is comparable with that of silicene, 5.3 × 105 m s−1. Their Berezinskii–Kosterlitz–Thouless transition temperatures are determined to be as high as 445 and 695 K. In addition, their half metallicity can be well maintained on h‐BN nanosheets and is immune to chemical perturbation and mechanical strain. Its fascinating magnetic properties and topological nodal lines render 2D Cr2X3 (X=O,S,Se) suitable for novel spintronic devices and exotic quantum applications.

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