The theory of piezoelectric photoacoustic spectroscopy is developed for condensed‐matter samples. Treating the sample as an elastic layer and neglecting the transducer’s effect on the sample, the three‐dimensional uncoupled quasistatic thermoelastic equations are solved using a Green’s function for the stress. An expression for the dependence of the signal on absorption, modulation frequency, thermal properties, and mechanical properties of the sample is derived. The theoretical predictions are experimentally verified, the sources of noise are analyzed, and the noise equivalent power is estimated. Finally, considerations for detector optimization are discussed.