A new technique is proposed for making phase diffraction gratings for integrated optics. The ion-exchange technique in glass is used, the grating is obtained by performing the ion exchange through a periodic mask photolithographically printed in aluminium. The required modulation of the index of refraction is obtained by introducing consecutively two different ions, Ag + and K+, inside the glass slide. The opto-geometric parameters of the phase diffraction grating are theoretically determined to obtain good wavelength demultiplexing properties at lambda1 = 0.6328 µm and lambda2 = 0.5145 µm. An experiment is performed where an incident light beam with two wavelengths, lambda1 and lambda2, is directed on the grating with an angle of incidence such that all the diffracted energy is transferred to the first order of diffraction for lambda1 and to the zeroth order for lambda2. The same device could easily be designed for wavelengths of interest in telecommunications systems