Maximum allowable transistor junction temperature. Silicon transistors normally have a maximum allowable junction temperature of 200 C. Devices packaged in plastic may have this value reduced to 150 C.

T_{j max} is an industry standard number based on projected lifetime; in most cases it does not represent a boundary to catastrophic failure of the transistor. Operation at temperatures above T_{j max} is not recommended as it will result in greatly decreased lifetimes since operating life is exponentially proportional to the inverse of the operating temperature.

T_{j max} may also be familiarly (though technically incorrectly) used to represent the maximum channel temperature (T_ch) of a GaAs FET.