- Theoretical and experimental results describing the dependence of the Seebeck and Peltier coefficients on the composition of Ga 1-x Al x As solid solution are given. The Seebeck coefficient for nondegenerately doped n‐ and p‐type Ga 1-x Al x As is given by the simple expressions α n =(k/e)(lnN c /n+2) and α p =-(k/e)(lnN v /p+2), respectively. The dependence of α on the composition of Ga 1-x Al x As solid solutions is linear for p type and nonlinear for n type. This relation is dependent on the type of carrier that is involved in the conduction process, as well as the detailed band structure of the material. For p‐type material, two kinds of carriers are involved: heavy and light holes; for n‐type material, three kinds of carriers are involved: one direct electron and two indirect electrons. The direct electrons are dominant for Al composition of 0≪x≪0.3, and the indirect electron is dominant for composition 0.45≪x≪1. Experimental measurements of the Seebeck coefficient for n‐ and p‐type Ga 1-x Al x As and for AuGe and AuZn resemble the theoretical results.