The measurement of absolute crystal polarity is crucial to understanding the structural properties of many planar defects in compound semiconductors. Grain boundaries, including twin boundaries, in the sphalerite lattice are uniquely characterized by the crystallographic misorientation of individual grains and the direction of the crystal polarity in domains adjoining the grain boundary. To evaluate crystal polarity in gallium phosphide (GaP), asymmetrical interference contrast in convergent-beam electron-diffraction (CBED) patterns was used to ascertain the nature and direction of polar bonds. The direction of the asymmetry in the electron diffraction reflections was correlated with the crystal polarity of a sample with known polarity. The CBED technique was applied to determine the polar orientation of grains adjoining Σ = 3 coherent and lateral twin boundaries in polycrystalline GaP.