This study aims to characterize two p-type HPGe detectors with the same geometric properties, which were put into operation 9 years ago by determining the optimum dead layer thickness. Experimental efficiencies were measured in the energy range of 81–1408 keV using point sources. As a result of simulations using general-purpose and specific-purpose Monte Carlo codes, optimized dead layer thicknesses, which were stated to be <1 mm after production, were 1.19 mm for Det1 and 1.71 mm for Det2. Experimental and Monte Carlo full energy peak efficiency values calculated with optimized dead layer thicknesses have the greatest difference of 5 %. The two detectors were characterized as a result of the optimized thicknesses determined by the Monte Carlo simulations. It was concluded that one reason for the variation in the dead layer specified by the manufacturer is vacuum degradation.