Nature Materials, Published online: 02 June 2026; doi:10.1038/s41563-026-02614-6Substantial strain hardening can be triggered in GaSe and other similar chalcogenide single crystals at particular loading directions inclined to the [0001] zone axis via alternating interlayer slip. This mechanism results in large uniform tensile elongation exceeding 40%, with the ultimate tensile elongation surpassing 70%.