The behavior of CdGa₂S₄ and CdGa₂Se₄ single crystalline semiconductors under Berkovich indentation of the (1 1 2) face in the load range of 10-700 mN has been investigated. Values of hardness and Young's modulus have been determined for this load range. A comparative analysis of crack development under indentation was performed for these two compounds. The observed indentation size effect was analyzed from the point of view of energy consumed for the formation of the residual imprint, fracture and relaxation processes. It was found that crack development affects the energy-load and hardness-load dependences, which show specific features for each compound. The effect of indentation on eventual phase transitions was investigated by comparing the micro-Raman spectra from a non-indented site with those measured in the indentation. Evidence of a phase transition under indentation from the initial defect chalcopyrite structure to a disordered zincblende phase is found.