A wireless power transfer system using a resonant rectifier circuit with capacitor sensing. A wireless power transfer system includes a power receiver resonant circuit and a synchronous rectifier. The power receiver resonant circuit includes an inductor and a capacitor connected in series with the inductor. The synchronous rectifier is configured to identify zero crossings of alternating current flowing through the inductor based on voltage across the capacitor, and control synchronous rectification of the alternating current based on timing of the zero crossings.