An extensive theoretical study has been made on the factors that influence the formation of native defects and extrinsic impurity incorporation in semiconductors. A complete set of reaction equations within equilibrium statistical mechanics is used to predict defect concentrations of intrinsic and extrinsic defects. The competing reactions involving host atoms include vacancies, antisites, and interstitial defects and the extrinsic impurity reactions include anion and cation site substitutional and interstitial site impurities. The extrinsic and intrinsic reactions form a coupled system. Examples are given to illustrate how various factors influence defect abundances, and such factors include temperature, stoichiometry, the host material, and the chemical potential of the electron/hole system. It is found that extrinsic impurities have a profound effect on native defect abundances. The defect formation energies used in the theory are obtained from a recently developed pseudoatomic‐orbital scheme using the local density approximation and pseudopotentials.