In GaN, the basal plane stacking fault type I1 is a two-dimensional defect characterized by a cubic inclusion within the wurtzite structure. Excitons are bound at the BSF I1 similar to the localization in a quantum well heterostructure leading to an efficient radiative recombination. In this study, we present the optical and structural properties of basal plane stacking faults occurrent in silicon doped a-plane GaN layer by means of highly spatially resolved cathodoluminescence spectroscopy performed in a scanning transmission electron microscope. Drastically reduced panchromatic intensity in the vicinity of partial dislocations terminating the stacking faults, points to their non-radiative character. Originating from intersection of two-dimensional defects, the emission at 379.6 nm could be attributed to optically active stair-rod dislocations.