Theoretical and experimental results describing the dependence of the Seebeck and Peltier coefficients on the composition of Ga1−xAlxAs solid solution are given. The Seebeck coefficient for nondegenerately dopedn‐ andp‐type Ga1−xAlxAs is given by the simple expressions &agr;n=(k/e)(lnNc/n+2) and &agr;p=−(k/e)(lnNv/p+2), respectively. The dependence of &agr; on the composition of Ga1−xAlxAs solid solutions is linear forptype and nonlinear forntype. 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. Forp‐type material, two kinds of carriers are involved: heavy and light holes; forn‐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 forn‐ andp‐type Ga1−xAlxAs and for AuGe and AuZn resemble the theoretical results.