This paper addresses the broadening mechanism of the near band gap photoluminescence in GaN films doped n-type with silicon. The films were produced by plasma assisted MBE and their carrier concentration was varied systematically from 1015 to 1020 cm−3. The photoluminescence was excited with a 10 mW He-Cd laser at 77K. At low carrier conentration ( < 1017 cm−3 ) the photoluminescence peak has FWHM of about 18 meV, while at high carrier concentration (>1018 cm−3 ) the FWHM increase monotonically with the carrier concentration up to about 120 meV. The broadening of the line at high carrier concentration is attributed to impurity band broadening and tailing of the density of states. The data were quantitatively analyzed, as a function of carrier concentration and compensation ratio, using the impurity band broadening model of Morgan  and the agreement between model and experimental data supports the model's validity and suggest a potential method of determining the compensation in degenerate semiconductors.