The application of n-type GaN thin films (thickness of 4.4 mu m) for measurement of the correlation spectrum of femtosecond laser pulses is demonstrated for the entire spectral region of the fundamental (720-820 nm) and second harmonic beams of a Ti:sapphire laser. Phase matching conditions are not required. The GaN thin film is stable and robust. Its wide band gap (3.4 eV) allows the characterization of femtosecond laser pulses over a wide wavelength range from 370 nm to 1.1 mu m.