Gallium nitride (GaN) and boron nitride (BN) are known as superior semiconductor materials for UV optoelectronic and high power, high temperature applications. As a result of their high molecular bond strength these materials are extremely difficult to etch. In this article, reactive ion etching (RIE) tests were performed on GaN and BN thin films using respectively BCl3/Cl-2/Ar and Cl-2/Ar chemistries. In order to improve the etch rates at lower rf powers and thus reduce ion bombardment-induced damage, a photoassisted RIE process was investigated. The same plasma chemistries in combination with a xenon are lamp were utilized. In an attempt to minimize surface nitrogen depletion, N-2 was used instead of Ar as dilution gas. Photoenhancement was observed for both GaN and BN etching. As expected, the etch rate increased with rf power for both unassisted and photoassisted etching conditions. The combination of illumination and N-2 led to a nitrogen-rich surface for GaN. In the case of BN, photoassisted etching in Ar resulted in a slightly lower surface nitrogen depletion. Chlorine was also detected on both etched GaN and BN films under illumination at a content of less than 1.7% and 2.5%, respectively.