Intermetallic titanium aluminides are promising for high temperature service. This is caused by their excellent creep behaviour and high oxidation resistance at service temperature. In addition, TiAl alloys exhibit a low density in comparison with currently used nickel-base superalloys. As a consequence, this class of materials is already introduced as turbine blades and turbocharger wheels. Thereby, β-solidifying γ-TiAl based alloys, e.g. TNM alloys, are used at service temperatures up to 750 °C. Upcoming TiAl alloying concepts should increase this application temperature, while maintaining the same mechanical load under adapting the alloy composition and process parameters. This study deals with new γ-TiAl based alloys, in which silicon was added. The starting material was produced in form of buttons by melting metallurgy. Thereby, the alloys solidify through a peritectic transformation, which is caused by the respective chemical composition. The silicon content was varied within these alloys. DSC and heat treatment experiments were conducted to gain information from the influence of alloying elements on the transition temperatures. As a result, a quasi-binary phase diagram was generated. Subsequently, a heat treatment was designed to generate a fine grained fully-lamellar microstructure. Therefore, several heat treatments were conducted, which took place within the α-single phase field region. During these heat treatments silicides prevent grain coarsening. This could also be observed by laser scanning confocal microscopy. After annealing within the α-single phase field region, the specimens were cooled down by different cooling rates. As a consequence, globular and massive γ-phase could be analysed in the microstructure at certain cooling rates. The resulting microstructures were aged to stabilise the lamellar α2/γ-structure. Afterwards, the stability of the microstructures was verified by long-term heat treatments at different temperatures. These microstructures were examined by REM, where a cellular reaction could be detected starting at massive γ grain boundaries. The present results provide thermodynamic information about the influence of the alloying elements on γ-TiAl. Furthermore, this knowledge will be used to enhance the service temperature by optimizing the chemical composition and heat treatments.