The analytical expression is derived for the time dependence of the total minority‐carrier content in a semi‐infinite semiconductor slab, after excitation with a delta function light pulse. It is shown that to this end it is sufficient to solve the continuity equation for the minority carriers in one dimension only. This implies that the excitation may have an arbitrary lateral spatial distribution. The photoluminescence, probing the total minority‐carrier content, turns out to be a nonexponential function of time when the surface/interface recombination velocity differs from zero. A practical method is developed to deduce accurate values of the bulk lifetime and the interface recombination velocity from such a nonexponential decay curve, based on a special way of plotting. Moreover, the analytical expressions are derived for the photoluminescence decay in the case of finite slab thicknesses and finite interface recombination velocities. From these results it is evident that only for large ratios (>10) of slab thickness and minority‐carrier diffusion length can the semiconductor be considered as being semi‐infinite.