A GaN compound semiconductor device can be capable of free process design and can have optimum device characteristics. The device can include a group III nitride compound semiconductor laminate structure including an n-type GaN compound semiconductor layer and a p-type GaN compound semiconductor layer. An n electrode can be formed on the n-type GaN compound semiconductor layer, and a p electrode can be formed on the p-type GaN compound semiconductor layer. The n electrode preferably includes an Al layer of 1 to 10 nm, in contact with the n-type GaN compound semiconductor layer, and any metal layer of Rh, Ir, Pt, and Pd formed on the Al layer. The p electrode can be made of a 200 nm or less layer of of Pd, Pt, Rh, Pt/Rh, Pt/Ag, Rh/Ag, Pd/Rh, or Pd/Ag, in contact with the p-type GaN compound semiconductor layer. Both electrodes can make ohmic contact with respective n-type/p-type GaN semiconductors without application of active annealing.