A surface acoustic wave device including a piezoelectric layer, an interdigital transducer electrode over the piezoelectric layer, and a polymeric roof layer arranged over the piezoelectric layer and interdigital transducer electrode. The polymeric roof layer is spaced apart from the piezoelectric layer to define a cavity to accommodate the interdigital transducer electrode. The polymeric roof layer is supported along a span of the polymeric roof layer by at least one pillar. The thermal conductivity of the pillar is greater than the thermal conductivity of the polymeric roof layer. Related wafer-level packages, radio frequency modules and wireless communication devices are also provided.