A systematic study was made of the relative stability and various phase changes which take place when elemental compound and mechanically mixed semiconductors are heated. These were chalcogens, calcogenides and mixtures of the two. The interest in the present investigation is due to the useful application of the prepared materials in the transistor, radar, rectifier and other electronic industries. Thermogravimetry and differential thermal analysis were carried out in air in the temperature range 20–830°. The results led to the conclusion that the degree of stability of the mechanically mixed semiconducting components is much higher than that of either elemental or compound semiconductors. The results were discussed on the basis of the electronegativity differences and oxygen affinities of the non-metallic components. The thermal stability ranges were evaluated in each case for the materials investigated, for their subsequent physical measurements and their suitability for the production of semiconducting devices.