Results of angle dispersive X-ray diffraction (ADXRD) measurements on the defect chalcopyrites (DCP), HgAl₂Se₄ and CdAl₂S₄ up to 22.2 and 34 GPa, respectively, are reported. The ambient tetragonal phase is retained in HgAl₂Se₄ and CdAl₂S₄ up to 13 and 9 GPa respectively. The values of the bulk modulus estimated from the Equation of State is 66(1.5) and 44.6(1) GPa for HgAl₂Se₄ and CdAl₂S₄ in the chalcopyrite phase. At higher pressure a disordered rock-salt structure and on pressure release a disordered zinc blende structure with broad X-ray diffraction lines are observed as is the case for several defect chalcopyrites.