Synthetic end-member strontium feldspar (SrAl₂Si₂O₈) has been studied in a diamond-anvil cell at elevated pressures up to 10.3 GPa using energy-dispersive X-ray powder diffraction. Cell parameters have been refined between ambient pressure and 6 GPa. SrAl₂Si₂O₈ undergoes a ferroelastic phase transition from the ambient pressure monoclinic space group I2/c to the high-pressure triclinic space group I1¯ at 3.2 ± 0.4 GPa. The transition appears to be first-order and the ferroelastic and co-elastic components of the spontaneous strain tensor have been calculated.