The deposition of GaN thin films in a nitrogen-hydrogen microwave plasma using Ga(CH3)(3) as a gallium precursor was investigated The deposit was identified as stoichiometric GaN by XPS and XRD. The substrate was dielectrically heated in the microwave discharge and the substrate temperature was lower than that in usual thermal MOCVD. The NH radicals, which were the primary N-atoms precursors, and fragments of Ga(CH3)(3) were identified in the plasma by OES. The NH radical formation and the decomposition of Ga(CH3)(3) in the plasma may be one of the reasons for the lower deposition temperature of GaN. The position dependence of the substrate temperature showed similar tendency as the position dependence of the electron temperature. The plasma state contributes to the deposition of GaN thin films. The deposited GaN exhibited a wide optical band gap of 3.4 eV. Material highly oriented along the c axis was detected in the deposit, and a PL spectrum which has the band head at about 450 mm was obtained.