In this letter, we propose a semiblind channel estimation technique for OFDM/OQAM wireless systems. The proposed technique exploits the real property of transmitted symbols to blindly identify the channel-induced rotation in the received signal, thereby reducing the pilot overhead for estimation purpose. Specifically, the channel phase over each subcarrier can be obtained from the spatial-sign covariance matrix of the received signal, while the channel amplitude can be expressed in terms of the subcarrier power. In effect, the frequency-domain noise can be reduced effectively by block averaging over multiple symbols. Since the channel delay spread is usually much smaller than the symbol duration, channel coefficients obtained from the estimated phase and amplitude can be further refined through low-rank filtering. Simulation results validate the efficacy of the proposed technique in time-dispersive fading channels, showing its robustness under different signal-to-noise ratio (SNR) conditions.