Micro-electro-mechanical comb-drive actuators made of GaN crystal are studied for an integrated a tunable GaN optical device. The GaN crystal was grown on a Si substrate by metal-organic chemical vapor deposition (MOCVD) with a low-temperature buffer layer. Selectively etching the Si substrate by XeF2 gas, the GaN thin crystal layers are self-supported in air. Due to the residual stress by the crystal growth, the freestanding GaN layer of actuator suffers from the considerable deformation depending on the growth conditions. To compensate the convex deformation, the crystallization tension of thin HfD2 film deposited on the GaN layer is used. The displacement is 1.3 �m at 70V. The fabricated GaN actuator can be useful for the monolithic integration for tunable GaN light sources.