The transition involving an exciton bound to an ionized donor has been identified in GaN. The linewidth of the transition was not sufficiently narrow to permit identification from Zeeman studies. Instead, an alternative series of measurements including energy ordering of the ionized-donor-bound exciton with respect to the neutral-donor-bound exciton, line widths of the above two excitons, screening studies and electron bombardment measurements were used to identify the transition. (C) 1997 Elsevier Science Ltd.