In a moderate temperature range (450–650 K), β-Zn_{3.83 + δ}Sb₃ has numerous advantages because the figure-of-merit (Z T) of β-Zn_{3.83 + δ}Sb₃ is the highest in this temperature range. However there are difficulties when attempting to control the stoichiometry so as to manufacture Zn_{3.83 + δ}Sb₃ specimens. In this study, three different compositions, Zn_3.83Sb₃ [δ (excess Zn) = 0], Zn_3.9Sb₃ (δ= 0.07), and Zn₄Sb₃ (δ= 0.17), were designed to obtain a β-Zn_{3.83 + δ}Sb₃ single phase through a hot-press sintering process. An investigation for the temperature dependence of thermoelectric properties confirmed that the Zn₄Sb₃ (δ= 0.17) composition hot-pressed at 723 K was the optimized condition for obtaining the Zn_{3.83 + δ}Sb₃ single phase representing best thermoelectric properties. As a result, a maximum Z T value of 1.33 was obtained at a measuring temperature of 664 K for the Zn₄Sb₃ (δ= 0.17) composition hot-pressed at 723 K.