This study presents the design and implementation of a 6.78 MHz wireless power transfer (WPT) system that uses magnetically coupled resonance for 5 W mobile phone charger applications. For a resonant WPT system, one of the most significant design issues is the power receiver because of its resonant characteristics. A compact resonant-type power receiver is required for high efficiency and robustness. To realise a compact size, a fully integrated 5 W power receiver that includes an on-chip AC-DC converter and a DC-DC converter is implemented. A protection circuit that operates only during initial power-up is proposed to protect the power switches in the receiver. The proposed receiver was implemented using a 0.18 mu m bipolar-complementary metal-oxide-semiconductor-double-diffused metal-oxide-semiconductor process with a die area of 3.5 mmx3.5 mm. The measured maximum power transfer efficiency of the receiver and peak efficiency of the system was 81 and 51%, respectively.