In this paper, an efficient wireless power transfer (WPT) design using near-field inductive 4-coil strongly-coupled-magnetic-resonance (SCMR) for powering up miniature biosensors at the ISM band of 5.8 GHz is proposed and analyzed. The miniature device has a tiny square planar inductor of size 110 × 110 μm as a receiver (RX) coil integrated on a standard silicon substrate. Another planar coil of 3 mm in diameter is designed on a FR4 substrate as the transmitting (TX) coil, which is fixed at 1 mm away from the RX coil in this study. The corresponding 4-coil SCMR system has the same TX and RX coils but with two relay coils between them, where the closest distance from the relay coil to the RX coil is also fixed at 1 mm. Analytic equations are used to describe the design for both scenarios, and 3-Dimensional (3-D) S-parameter and B-Field electromagnetic (EM) simulations show that the optimized 4-coil system consistently outperforms the optimized 2-coil WPT system by ∼6-7 dB, reaching an impressive inductive power coupling of ∼ -20.2 dB (i.e., ∼ 1% power transfer efficiency) unto the tiny RX coil for potentially powering up novel implantable and other miniature devices without bulky batteries.