A novel two-stage sulfur diffusion technique for doping crystalline silicon has been developed and experimentally validated. The main advantage of the proposed method is the almost complete suppression of surface erosion, which is one of the most critical drawbacks of conventional high-temperature diffusion processes. Systematic studies were carried out on Czochralski-grown p-type silicon samples with different initial boron concentrations, under controlled sulfur vapor pressures ranging from 1.16 atm to 7.32 atm. Electrical parameters were investigated using the Hall effect method, and the total concentration of electroactive sulfur atoms was determined from charge neutrality equations, taking into account the Fermi level position.The results demonstrate that the initial boron concentration has virtually no effect on the incorporation of electroactive sulfur atoms at constant sulfur vapor pressure. In contrast, a strong dependence on sulfur vapor pressure was established: an increase from 1.16 atm to 7.32 atm resulted in nearly a two-order-of-magnitude rise in the concentration of electroactive sulfur atoms, exceeding the maximum values previously reported in the literature by approximately 1.4 orders of magnitude. Complementary studies using SIMS/ToF-SIMS, Raman, and TEM analyses confirmed the distribution of sulfur atoms, the formation of defect-related states, and the microstructural modifications induced by diffusion. These findings highlight the efficiency of the two-stage diffusion approach and its potential for achieving ultrahigh impurity concentrations. From a practical perspective, the method significantly broadens the functionality of sulfur-doped silicon, particularly for the development of infrared photodetectors and highly stable thermal sensors.