An integrated experimental study and thermodynamic modelling approach has been used in the investigation of the distribution of As between slag and matte in equilibrium with tridymite in the Cu-Fe-O-S-Si system. The experimental technique involves high-temperature equilibration in sealed quartz ampoule, rapid quenching, and direct measurements of phase compositions using microanalysis techniques. Electron Probe X-ray Microanalysis (EPMA) was used to measure major and minor element concentrations in the matte, slag, and solid phases. The experimentally-determined distribution coefficient of As between slag and matte was found to decrease with decreasing P(SO2) from log L = 0.5 at P(SO2) = 25 kPa to approximately log L = -4.0 at lowest P(SO2), corresponding to metal saturation. Thermodynamic model parameters describing As distribution have been derived based on the present and previous data on the slag/matte, slag/metal, and slag/matte/metal equilibria. The thermodynamic model can be used for the evaluation of distribution of As between phases in the high-temperature pyrometallurgical production and refining of copper. (C) 2019 Elsevier Ltd.