It is of particular importance to characterise spectrally each component in the chemical systems in which the reaction proceeds or when the two forms of the same compound exist in equilibrium (tautomerism, cis-trans isomerism, dissociation, etc.). Moreover, physical or chemical separation of the component that is in a smaller amount is always difficult, as well as recording its spectrum. A new simple numerical method of extraction of overlapped spectra of two components is presented. It was termed SEMILAM, which stands for ‘separation by minimum overlapping method’. This method can be applied when two spectra of the same sample consisting of two species can be recorded. These spectra have to differ in composition but total concentration has to maintain constant. In other words, the data required to apply the method comes from one sample for which the two spectra were recorded at two different points of time (the composition of the sample has to change). Knowledge of real fractions found in the crude plots is sufficient to extract quantitatively the spectra of pure components. This new simple method was successfully tested on simulated spectra and then applied to a real problem.