The hard x‐ray photoacoustic signal intensities of copper have been measured at an x‐ray absorption near‐edge structure (XANES) region as functions of sample thickness (from 5 to 300 &mgr;m) and modulation frequency (from 5 to 50 Hz). It is shown that the photoacoustic signal intensities show maxima at the sample thickness close to 10 &mgr;m for each modulation frequency. The x‐ray photoacoustic signal varies fromf−1.0( fdenotes modulation frequency) up to 20 &mgr;m sample thickness, whereas it varies fromf−0.5beyond a 20 &mgr;m sample thickness, which is not consistent with the Rosencwaig–Gersho theory for the photoacoustic effect in solids.