In this study, a constant-power inductive-coupling transmitter for low-power supply-sensing biosensing platforms is proposed. The proposed inductive-coupling transmitter is composed of two driving transistors with different inputs from different pulse generators. The two pulse generators have different working threshold voltages, and one of them works as the main driving switch, while the other works as an auxiliary driving switch, which turns on only at low supply voltages. This auxiliary driving technique realizes the constant power characteristics of the inductive-coupling transmitter because the auxiliary driving transistor only functions at low supply voltages, which reduces waste power at high supply voltages. To verify the effectiveness of the proposed inductive-coupling transmitter, a test chip is fabricated using 65 nm silicon-on-thin-box (SOTB) CMOS technology. The test chip successfully demonstrates constant power characteristics, whereas the power consumed by the conventional inductive-coupling transmitter increases with an increase in the supply voltage.