<p>Superconducting diodes promise low-dissipation rectification for superconducting electronics and low-temperature applications. Generating a quantized d.c. voltage from radio-frequency (rf) irradiation without external bias could enable self-powered cryogenic devices but are challenging to realize. Here we use the kagome superconductor CsV₃Sb₅ to demonstrate quantized rf rectification at zero magnetic field. We fabricate transport devices from mechanically exfoliated single-crystal nanobeams with a thickness of 100–200 nm and a width of 1 μm contacted by gold electrodes. These devices exhibit Josephson effects, probably originating from intrinsic weak links within the material, and show Josephson diode effects even at zero external magnetic field. Under rf irradiation without a current bias, a d.c. voltage emerges and scales linearly with the microwave frequency <i>f</i> as <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({V}_{{\rm{d.c.}}}={hf}/2e\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mrow> <mi>V</mi> </mrow> <mrow> <mi mathvariant="normal">d.c.</mi> </mrow> </msub> <mo>=</mo> <mi mathvariant="italic">hf</mi> <mo>/</mo> <mn>2</mn> <mi>e</mi> </mrow> </math></EquationSource> </InlineEquation>, where <i>h</i> is Planck’s constant and <i>e</i> is the electron charge. At constant frequency, the voltage increases in quantized steps with increasing rf power, consistent with the emergence of Shapiro steps. Our work establishes CsV₃Sb₅ as a potential platform for cryogenic-temperature wireless power sources and self-powered voltage standards.</p>