Wire-like structures are found to form on the GaAsN surfaces. The wire heights and intervals are dependent on the N composition and are typically similar to 10 and similar to 50 nm, respectively. The wires were facetted with (1 1 n)A crystal planes, where a value of "n" is in the range of 3-9 and is reduced with increasing N composition. Transmission electron microscopic examination shows that the lateral compositional modulation is correlated with the surface-wire-like structure. The formation mechanism is discussed based on the site-selective N incorporation at the A-steps on the wired surfaces.