The present application describes embodiments of a radio-frequency identification (RFID) sensor based on a combinationof a surface acoustic wave (SAW) transducer and two-dimensional electron gas (2DEG) or two-dimensional hole gas (2DHG) conducting structure, and its use in chemical detection and (bio)molecular diagnostics. The SAW RFID sensor chip contains apiezoelectric substrate, on which a multilayer heterojunction structure is deposited. The heterojunction structure comprises atleast two layers, a buffer layer and a barrier layer, wherein both layers are grown from III-V single-crystalline or polycrystallinesemiconductor materials, such as GaN/AlGaN. Interdigitated transducers (IDTs) transducing SAWs are installed on top of thebarrier layer. A 2DEG or 2DHG conducting channel is formed at the interface between the buffer and barrier layers and provideselectron or hole current in the system between the non-ohmic (capacitively-coupled) source and drain contacts connected to the formed channel.