An FAAS method for the determination of mass ratio of chemical composition in thin film transistors (TFT) of CdSe is proposed in this paper. Pure CdSe was used as common standard sample of Cd and Se in the separate experiment. Measured value of total weight and mass ratio of chemical composition for CdSe powder

and measured value of TFT film sample were tested separately in order to check the accuracy of this method. Their relative errors are 0.42%

-3.8% and -0.5%

respectively. The results show that this method can meet the need of accuracy. Because disturbing effects between two elements are eliminated in the determination process using a common standard sample

the accuracy of determination with this method is better than that using two different standard samples. Disturbance and recovery experiments are not necessary to do because both sample and standard are the same approximately in component and concentration. Quality and influence factors of CdSe TFT can be explained by measured value. If measured weight of CdSe matches formula weight

then the operation sequences are rational and the quality of thin film is better (shown by the results of Sample a

#

). As pressure of saturated vapor of Se is higher than that of Cd

Se is more volatilizable than Cd. Concentration of Se in CdSe powder left over evaporating dish is decreased with increasing times of film deposition. The samples of 3

#

、4

#

are typical examples. Analytic results have proved this conclusion.