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Surface acoustic waves (SAWs) that propagate on the surface of a solid at MHz frequencies are widely used in sensing, communication, and acoustic tweezers. However, their properties are difficult to be tuned electrically, and current devices suffer from complicated configurations, complicated tuning mechanisms, or small ranges of tunability. Here a structure featuring a thin‐film transistor configuration is proposed to achieve electrically tunable SAW propagation based on conductivity tuning. When a DC gate voltage is applied, the on‐site conductivity of the piezoelectric substrate is modulated, which leads to velocity and amplitude tuning of SAWs. The use of carbon nanotubes and crystalline nanocellulose as the channel and gate materials results in high tuning capacity and low gate voltage requirement. The tunability is manifested by a 2.5% phase velocity tuning and near 10 dB on/off switching of the signals. The proposed device holds the potential for the next generation SAW‐based devices.