We studied the thermoelectric properties of free-standing GaN (fr-GaN) and epitaxial GaN layer (epi-GaN), and furthermore, we have fabricated thermoelectric devices using these materials. For fr-GaN, the maximum power factor was 7.7 x 10(-4) W/m K-2 at 373 K, and for epi-GaN layer, the maximum power factor was 9.4 x 10(-4) W/m K 2 at 373 K. The devices fabricated are (a) fr-GaN and chromel of 4 pairs, and (b) epi-GaN and chromel of 3 pairs. The maximum output power and the open output voltage were (a) 3.35 x 10(-6) W and 2.76 x 10(-2) V at Delta T=153 K, and (b) 1.21 X 10(-7) W and 1.71 X 10(-2) V at Delta T=153 K, respectively. (c) 2006 Published by Elsevier B.V.