Abstract <p>High-purity arsenic is required for the synthesis of A^IIIB^V compounds and their solid solutions, which serve as the basis for semiconductor heteroepitaxial structures used in optoelectronics, laser technology, solar energy and microelectronics. In this regard, calorimetric studies were conducted to examine the effects of temperature and arsenic acid concentration on the thermal properties (specific heat capacity, thermal conductivity and thermal diffusivity) of solutions in the H₃AsO₄–H₂O system over a wide range of temperatures (20–80°C) and H₃AsO₄ concentrations (18.95–81.45 wt %). The obtained data may be useful for designing the arsine electrochemical synthesis for the subsequent high-purity arsenic production.</p>