Optical absorption measurements were performed on a series of thin GaN epilayers. Sharp spectral features were observed due to the1sAandBexciton transitions. Using polarization dependent absorption, theCexciton transition was identified. A broad absorption feature was observed at ∼3.6 eV, which is attributed to indirect exciton-phonon absorption. The excitonic structure was found to persist well above room temperature. A fit to the Varshni formula yielded a temperature dependence ofE(T)=E(T=0)−11.8×10−4T2(1414+T)eV for theAandBexcitons. The exciton absorption linewidth was studied as a function of temperature, indicating that GaN exhibits very large exciton-phonon coupling. ©1997 American Institute of Physics.