Field-effect transistor (FET) biosensors are suitable for use in miniaturized and cost-effective healthcare devices. These biosensors use various semiconductive materials, including one- and two-dimensional materials, as FET channels. The signal transduction interface between the biosample and the FET channel is crucial for translating electrochemical reactions into output signals, enabling the detection of target ions or biomolecules. This review discusses distinctive signal transduction interfaces for FET biosensors, categorized as chemically synthesized, physically structured, and biologically induced interfaces. These interfaces are key in controlling biosensing parameters such as specificity, selectivity, binding constant, limit of detection, signal-to-noise ratio, and biocompatibility. A solution-gated FET biosensor is suitable for miniaturized and cost-effective systems to directly measure biological samples in in vitro diagnostics. These devices can be easily equipped with wireless functions and attached to the body, enabling wearable biosensors to detect biomarkers in tears, sweat, and saliva. The gate insulator surface (e.g., SiO₂) is directly in contact with the measurement solution in FET biosensors, unlike metal-oxide-semiconductor (MOS) transistors, where the potential of the measurement solution is controlled by a reference electrode. When ions or biomolecules with charges are adsorbed on the gate insulator surface, their charges electrostatically interact with electrons across the gate insulator, resulting in a change in the conductivity of the FET channel. This change in conductivity is detected as a change in the drain-source current (I_DS), which is potentiometrically measured. Oxide and nitride membranes (e.g., Ta₂O₅ and Si₃N₄) used as gate insulators contribute to the detection of pH changes based on the equilibrium reaction between hydrogen ions and hydroxy groups at their surfaces. Various ion-sensitive membranes (ISMs) and biological receptors with enzymes, antibodies, and single-stranded DNAs were modified on the gate electrode of FET biosensors to specifically and selectively detect target ions and biomolecules. These biosensors can monitor cellular activities in real-time by detecting changes in ion concentration. The detection principle of FET biosensors is based on the potentiometric measurement of changes in ionic and biomolecular charges or membrane capacitances at the gate electrode/electrolyte solution interface. One-dimensional (1D) and two-dimensional (2D) semiconductive materials have been proposed for the channel of FETs for biosensing devices. A solution-gated 1D or 2D-channel FET biosensor with a steep subthreshold slope (SS) contributes to ultrahigh sensitive biosensing due to a relatively large electric double-layer capacitance at the electrolyte solution/channel interface. Thin-film transistors with transparent amorphous oxide semiconductors can be applied as one of the FET biosensors, deposited on transparentField-effect transistor (FET) biosensors are suitable for use in miniaturized and cost-effective healthcare devices. These biosensors use various semiconductive materials, including one- and two-dimensional materials, as FET channels. The signal transduction interface between the biosample and the FET channel is crucial for translating electrochemical reactions into output signals, enabling the detection of target ions or biomolecules. This review discusses distinctive signal transduction interfaces for FET biosensors, categorized as chemically synthesized, physically structured, and biologically induced interfaces. These interfaces are key in controlling biosensing parameters such as specificity, selectivity, binding constant, limit of detection, signal-to-noise ratio, and biocompatibility. A solution-gated FET biosensor is suitable for miniaturized and cost-effective systems to directly measure biological samples in in vitro diagnostics. These devices can be easily equipped with wireless functions and attached to the body, enabling wearable biosensors to detect biomarkers in tears, sweat, and saliva. The gate insulator surface (e.g., SiO₂) is directly in contact with the measurement solution in FET biosensors, unlike metal-oxide-semiconductor (MOS) transistors, where the potential of the measurement solution is controlled by a reference electrode. When ions or biomolecules with charges are adsorbed on the gate insulator surface, their charges electrostatically interact with electrons across the gate insulator, resulting in a change in the conductivity of the FET channel. This change in conductivity is detected as a change in the drain-source current (I_DS), which is potentiometrically measured. Oxide and nitride membranes (e.g., Ta₂O₅ and Si₃N₄) used as gate insulators contribute to the detection of pH changes based on the equilibrium reaction between hydrogen ions and hydroxy groups at their surfaces. Various ion-sensitive membranes (ISMs) and biological receptors with enzymes, antibodies, and single-stranded DNAs were modified on the gate electrode of FET biosensors to specifically and selectively detect target ions and biomolecules. These biosensors can monitor cellular activities in real-time by detecting changes in ion concentration. The detection principle of FET biosensors is based on the potentiometric measurement of changes in ionic and biomolecular charges or membrane capacitances at the gate electrode/electrolyte solution interface. One-dimensional (1D) and two-dimensional (2D) semiconductive materials have been proposed for the channel of FETs for biosensing devices. A solution-gated 1D or 2D-channel FET biosensor with a steep subthreshold slope (SS) contributes to ultrahigh sensitive biosensing due to a relatively large electric double-layer capacitance at the electrolyte solution/channel interface. Thin-film transistors with transparent amorphous oxide semiconductors can be applied as one of the FET biosensors, deposited on transparent