Application of the Semenov theory of spontaneous ignition to evaluation of the critical temperature (Tc′) in thermal explosion (TE) synthesis was conducted with the Ti-75at pct Al binary system using nonisothermal differential scanning calorimetry (DSC) at different heating rates. And the critical temperature for isothermal TE is predicted to be 728.9°C by the multiple linear regression of Tc′s evaluated according to Semenov theory, which is close to the range of 740～745°C obtained from the isothermal DSC observation. This result proves that Semenov theory of spontaneous ignition is also feasible for TE synthesis in binary metallic systems like Ti-75 at. pct Al system.