The first experimental verification of phase‐matched SHG was performed in the polycrystalline ZnS thin‐film waveguide deposited on a BK‐7 glass substrate. The complete phase‐matching between the TE1mode at the fundamental frequency of 1.054 &mgr;m and the TM4mode at its second harmonic wave was realized by using a tunable optical parametric oscillator. The interaction length estimated from the tuning curve for the phase matching was about 35 &mgr;m and the output harmonic power was of the order of milliwatts at 300‐W fundamental input under the phase‐matched condition.